Synthesis and NMR characterization of the novel mixed-ligands Pt(II) complexes Pt(amine)(pyrimidine)X2 and trans,trans-X2(amine)Pt(μ-pyrimidine)Pt(amine)X 2 (X = I and Cl)

Inorganica Chimica Acta 363 (2010) 1679–1693

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Inorganica Chimica Acta

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Synthesis and NMR characterization of the novel mixed-ligands

Pt(II) complexes Pt(amine)(pyrimidine)X₂and

trans,trans-X₂(amine)Pt(l-pyrimidine)Pt(amine)X₂(X = I and Cl)

*

Fernande D. Rochon , Hyem Titouna

Chemistry Department, Université du Québec à Montréal, C. P. 8888, Succ. Centre-ville, Montréal, Canada H3C 3P8

a r t i c l e i n f o

a b s t r a c t

Article history:

Mixed-ligand complexes of the type Pt(amine)(pm)I₂, (pm = pyrimidine) were synthesized and character-

ized by IR spectroscopy and by multinuclear (¹⁹⁵Pt, ¹H and ¹³C) magnetic resonance spectroscopy. The cis

Received 21 October 2009

Accepted 5 December 2009

Available online 12 January 2010

compounds were prepared from the reaction of I(amine)Pt(l-I)₂Pt(amine)I with pyrimidine (1:2 propor-

tion) in water, while the trans isomers were synthesized from the isomerization of the cis complexes in

acetone. The cis isomers could not be isolated with several amines, especially the more bulky ones. In ¹H

NMR, the pyrimidine protons of the cis compounds were found at lower ﬁelds than those of the trans ana-

logs and the J(¹⁹⁵Pt–¹H) coupling constants are slightly larger in the cis geometry. For n-butylamine, the

Keywords:

Platinum complexes

Synthesis

NH₃

reaction produced also I₂(n-butylamine)Pt(l-pm)Pt(n-butylamine)I₂. No such dimer could be isolated

with the other amines. The compounds Pt(amine)(pm)Cl₂were also prepared (amine = methylamine

and t-butylamine) from the ionic complex K[Pt(amine)Cl₃] using an excess of pyrimidine. The IR and

NMR characterization showed that the methylamine compound was a cis–trans mixture, while only

the trans isomer was isolated with t-butylamine. When the same reaction was performed using a Pt:pm

Amine

Pyrimidine

NMR

IR

ratio of 2:1, Cl₂(amine)Pt(

ﬁed by IR and multinuclear magnetic resonance spectroscopies as the trans–trans isomers. The trans

monomers and dimers showed only one

(Pt–Cl) band. The ¹⁹⁵Pt NMR signals of the dimers were found

close to those of the monomer trans-Pt(amine)(pm)Cl₂.

l-pm)Pt(amine)Cl₂was isolated. The pyrimidine-bridged dimers were identi-

m

1. Introduction

tortion of the DNA molecule. A few other studies also indicate that

dinuclear Pt(II) complexes might have a promising future in che-

motherapy [8].

Pyrimidine (pm) is a diazine like pyrazine and can form bridges

between two Pt atoms. A few pyrimidine-bridged-Pt(II) com-

The antitumor compound cisplatin (cis-Pt(NH₃)₂Cl₂) has now

been known for several decades and it is still one of the most com-

monly used drug for cancer treatment. Its mechanism of action is

extremely complex and there are still many uncertainties,

although the antitumor properties are known to be related to a

reaction with the bases (particularly guanine) of cellular DNA. A

few good reviews have been published [1,2]. When the NH₃ligands

of cisplatin are replaced by an amine, the compounds cis-Pt(ami-

ne)₂Cl₂are also quite active. The cyclic amines Pt(II) compounds

are more active than cisplatin, but they are much more insoluble

[3,4]. The mixed-ligand compounds cis-Pt(cyclic amine)(NH₃)Cl₂

are also very active, especially the cyclobutylamine complex

[5,6]. The pyrazine-bridged dinuclear Pt(II) complex cis,cis-

pounds were reported, like K₂[Cl₃Pt(

l

-pm)PtCl₃], Cl₂(R₂SO)Pt(

l-

pm)Pt(R₂SO)Cl₂[9] and Cl₂(Ypy)Pt(l-pm)Pt(Ypy)Cl₂, where

Ypy = pyridine derivative [10]. Pyrimidine and its derivatives are

interesting molecules and they play an important role in several

*

biological processes. The molecule contains some empty

p orbi-

tals, which could accept electron density from a soft metal like

Pt(II), but the nature of the Pt-pyrimidine bond has not yet been

studied in the literature. However, only a few papers were pub-

lished on platinum compounds with non-substituted pyrimidine.

Fazakerley and Koch [11] synthesized and characterized cis-

[Pt(NH₃)₂(pm)₂](ClO₄)₂by ¹³C NMR spectroscopy while Rochon

and coworkers [12] prepared cis- and trans-Pt(pm)₂X₂(X = Cl and

Br) and determined the crystal structures of the two trans isomers.

Kaufmann et al. characterized trans-Pt(PEt₃)(pm)Cl₂by ³¹P and ¹H

NMR, although they were not able to isolate the compound [13].

These authors also reported the pm-bridged compound trans,-

[Cl(NH₃)₂Pt(l-pz)Pt(NH₃)₂Cl]Cl₂was recently found to possess

good anticancer properties and seems to overcome the cross-resis-

tance of cisplatin [7]. The dinuclear compound has the appropriate

Pt–Pt distance and the ﬂexibility to react with a minimum of dis-

* Corresponding author. Tel.: +1 514 987 3000x4896; fax: +1 514 987 4054.

E-mail address: rochon.fernande@uqam.ca (F.D. Rochon).

trans-Pt(PBu₃)Cl₂(l-pm)Pt(PBu₃)Cl₂. More recently, we have

doi:10.1016/j.ica.2009.12.010

1680

F.D. Rochon, H. Titouna / Inorganica Chimica Acta 363 (2010) 1679–1693

published the synthesis of cis- and trans-Pt(R₂SO)(pm)Cl₂[14],

trans-Pt(R₂SO)(pm)I₂[15,16], cis- and trans-Pt(Ypy)(pm)Cl₂[10],

2.1. Synthesis and characterization of the iodo complexes

The diiodo-bridged dimers I(amine)Pt( -I)₂Pt(amine)I were

prepared from the method described in the literature [17,18].

In the following data, the pm IR assignments are based on the

most recent paper in the literature [19], the vibration numbers

are placed in parentheses and the frequencies are in cm^ꢀ1. The rel-

ative intensities are indicated by w (weak), m (medium) or s

(strong). The pyrimidine bands of the pure iodo compounds are

and the dinuclear species mentioned above K₂[Cl₃Pt(

Cl₂(R₂SO)Pt( -pm)Pt(R₂SO)Cl₂(the cis–cis and trans–trans isomers)

[9] and trans,trans-Cl₂(Ypy)Pt( -pm)Pt(Ypy)Cl₂[10].

l-pm)PtCl₃],

l

We have now started a new study of mixed-ligand Pt(II) com-

pounds containing an amine and pyrimidine. Amines are different

from sulfoxides and pyridine derivatives, since they cannot accept

electron density from the metal, although

p-bonding does not

seem to play a very important role in the Pt–pyridine bond.

The amine ligands used in this work have different bulkiness

around the N-donor atom. Steric hindrance is quite important

and is a major factor in the geometry of the mixed-ligand Pt(II)

compounds. For example, it is not possible to synthesize cis com-

pound with t-butylamine. We have now developed methods to

synthesize cis- and trans-Pt(amine)(pm)I₂. Diiodo compounds are

important, since they are more soluble in organic solvents that

the dichloro analogs, but IR spectroscopy is also less informative,

listed in Table 1, and the suggested m(Pt–N) vibrations are shown

in Table 2. The NMR signals are in ppm and the coupling constants

are in Hz. When a cis–trans mixture was obtained, the NMR spectra

of the pure trans complex is described later in the section. The lat-

ter signals were subtracted from the spectrum of the mixture, in

order to obtain the signals of the cis compounds. Most of the cou-

pling constants J(¹⁹⁵Pt–¹H,¹³C) are listed in the tables.

2.1.1. Pt(amine)(pm)I₂(amine = NH₃, MeNH₂, EtNH₂, n-propylamine

(nPrNH₂), n-butylamine (nBuNH₂), iso-propylamine (isoPrNH₂),

dimethylamine (Me₂NH), diethylamine (Et₂NH), cyclopropylamine

(cprNH₂), cyclobutylamine (cbNH₂), cyclopentylamine (cpNH₂) and

cyclohexylamine (chNH₂)

since the

that the

m

(Pt–I) vibrations are observed at much lower energies

m

(Pt–Cl) vibrations. We have also developed two methods

to prepare the dichloro analogs Pt(amine)(pm)Cl₂. The ﬁrst method

is useful only with bulky amines, while the second is more general.

We are also reporting a method to synthesize the pm-bridged

The

diiodo-bridged

dimer

I(amine)Pt(l-I)₂Pt(amine)I

dinuclear species Cl₂(amine)Pt(l-pm)Pt(amine)Cl₂. All the new

(0.2 mmol) is suspended in a minimum quantity of water (3–

5 mL). A small excess of pyrimidine (dissolved in a small quantity

of water) is slowly added (0.42 mmol). The reaction mixture is stir-

red at room temperature in the dark during 2–70 days (indicated

below for each complex), until there is no more change of color

(from brown to yellow).

compounds were characterized by IR and multinuclear magnetic

resonance spectroscopies. We have found that these techniques

are usually good methods to determine the geometry of the differ-

ent isomeric forms. The results of this study are reported below.

2. Experimental

Table 2

Frequencies of the

in the pure complexes cis-Pt(MeNH)(pm)I₂and trans-Pt(amine)(pm)I₂.

m

(Pt–N) (cm^ꢀ1) in the cis- and trans-Pt(amine)(pm)I₂mixture and

K₂[PtCl₄] was obtained from Johnson Matthey Inc. and was puri-

ﬁed by recrystallization in water before use. Pyrimidine and the

amines were obtained from Aldrich. Potassium iodide was bought

from Analar and CD₃COCD₃was purchased from CDN Isotopes.

The decomposition points were measured on a Fisher–Johns

instrument and were not corrected. The IR spectra were recorded

in the solid state (KBr pellets) on a FTIR Nicolet 4700 spectrometer

between 4000 and about 280 cm^ꢀ1. All the NMR spectra were mea-

sured in CD₃COCD₃on a Varian Gemini 300BB spectrometer oper-

ating at 300.07, 75.460 and 64.268 or 64.326 MHz for ¹H, ¹³C and

¹⁹⁵Pt, respectively. For ¹⁹⁵Pt, the external reference was K₂PtCl₄

in D₂O, adjusted at ꢀ1628 ppm from K₂PtCl₆(d(Pt) = 0 ppm) or

K[Pt(DMSO)Cl₃] in D₂O (d(Pt) = ꢀ2998 ppm).

Amine

cis- and trans-Pt(am)(pm)I₂

trans-Pt(amine)(pm)I₂

NH₃

503, 471, 453, 438

490, 465, 450, 435

500, 469, 453, 438

471, 453

cis: 490, 450

501, 471

500, 472

501, 472

502, 472

502, 469

502, 471

502, 473

503, 473

502, 472

MeNH₂

EtNH₂

nPrNH₂

isoPrNH₂

Me₂NH

Et₂NH

cprNH₂

cbNH₂

cpNH₂

chNH₂

502, 472, 453, 438

503, 471, 453, 438

502, 473, 453, 438

Table 1

Tentative assignment of the pyrimidine vibrations in free pyrimidine [19] and in the pure complexes cis-Pt(MeNH₂)(pm)I₂and trans-Pt(amine)(pm)I₂.

m_x

Free pm

MeNH₂

nPrNH₂

isoPrNH₂

EtNH₂

Me₂NH

Et₂NH

NH₃

cprNH₂

cbNH₂

cpNH₂

chNH₂

20a

2

7b, 13

8b

8a

19b

19a

3

15

9a

18b

12

1

10b

4

3076

3047

3035

1576

1566

1476

1403

1237

1161

1143

1084

1064

991

3090m

3060m

3029w

1580s

1540s

1450m

3087w

3053w

3026w

1590m

1576w

1467m

1405s

1217m

1154w

1129w

1088w

1055w

1026w

827m

3087w

3053w

3027w

1590s

1576w

1467m

1405s

1218m

1168m

1128w

1087w

1056m

1026m

827s

3087w

3054w

3027w

1591s

1554m

1466m

1404s

1218w

1169w

1129w

1088w

1056w

1027m

826m

3086s

3054w

3026w

1591s

1554s

1467m

1405s

1218w

1169w

1129w

1088m

1056m

1027m

827m

3073w

/

3088w

3069w

3030w

1590s

1551m

1466m

1404s

1227w

1172w

1127s

1088w

1058m

1027m

819s

3088w

3067w

3031w

1592s

1560m

1460m

1406s

1216w

1182w

1129w

1088w

1057w

1028w

814m

3087w

3054w

3023w

1591s

1576w

1466m

1405s

1215w

1169w

1129w

1098w

1056w

1027w

826m

3087w

3053w

3027w

1590m

1554m

1467m

1405s

1217w

1169w

1128w

1087w

1056m

1027m

827s

3087w

3054w

3025w

1590s

1570m

1468m

1405s

1243w

1152m

1128w

1087w

1055w

1026w

827s

1590m

1554m

1465m

1407m

1224m

1141m

/

1088w

1049w

1023w

827s

1185w

1140w

1070w

1057m

1000m

830w

700m

681m

650m

832

721

676

628

702s

680m

642m

702w

680s

642s

701s

678m

642m

702s

678m

642m

705m

682w

645m

703s

680m

645m

698m

678s

643m

702m

681w

642m

702s

680m

642s

702s

681w

642s

6a

6b

F.D. Rochon, H. Titouna / Inorganica Chimica Acta 363 (2010) 1679–1693

1681

2.1.1.1. Pt(NH₃)(pm)I₂. A 70% cis and 30% trans mixture was ob-

2.1.1.6.

Trans-Pt(isoPrNH₂)(pm)I₂. Reaction

time

70 days,

tained after 8 days of reaction. Yield = 87%, dec. = 165–220 °C. IR:

pm (20a) 3085w, (2) 3061w, (7b, 13) 3023w, (8b) 1588m, (8a)

1555s, (19b) 1465m, (19a) 1402s, (3) 1226w, (15) 1172w, (9a)

1128w, (18b) 1086w, (12) 1054w, (1) 1024m, (10b) 821s, (4)

yield = 84%, dec. = 154–180 °C. IR: isoPrNH₂m(NH) 3204w, 3268w,

m

(C–H) 3026fw, 3000w, d(NH) 1576w, 1554 m, d(CH₃) 1467 m,

1461 m. NMR: ¹H: pm H₂9.646s, H₆9.287ddd, ³J(H₆–H₅) = 6,

⁴J(H₆–H₄) = 2.1, ⁴J(H₆–H₂) = 1.2, H₄8.885dd, ³J(H₄–H₅) = 7.2, H₅

7.708ddd, ⁵J(H₅–H₂) = 0.9. isoPrNH₂NH 4.030s, H1 3.785 m, H2

1.282d ³J(H2–H1) = 6.6. ¹³C: pm C₂163.84, C₆163.20, C₄159.33,

C₅123.56. isoPrNH₂C1 51.39, C2 25.65.

703s, (6a) 680s, (6) 641s. NH₃m(NH) 3260w, d(NH) 1551 m. Cis iso-

mer: NMR: ¹H: pm H₂9.706s, H₆9.335ddd, ³J(H₆–H₅) = 5.7, ⁴J(H₆–

H₄) = 2.0, ⁴J(H₆–H₂) = 0.9, H₄8.919dd, ³J(H₄–H₅) = 7.2, H₅7.705ddd,

⁵J(H₅–H₂) = 1.2. NH₃NH 4.121s. ¹³C: pm C₂161.57, C₆160.72, C₄

159.66, C₅124.21.

2.1.1.7. Pt(Me₂NH)(pm)I₂. A 90% cis and 10% trans mixture was ob-

tained after 25 days of reaction. Yield = 85%, color change 145 °C,

dec. = 155–175 °C. IR: pm (20a) 3085w, (2) 3060w, (7b, 13)

3024w, (8b) 1588s, (8a) 1551m, (19b) 1465m, (19a) 1403s, (3)

1219w, (15) 1174w, (9a) 1128w, (18b) 1086w, (12) 1070w, (1)

1024m, (10b) 822m, (4) 702s, (6a) 681w, (6b) 641m. Me₂NH

2.1.1.2. cis-Pt(MeNH₂)(pm)I₂. Reaction time: 2 days, yield = 84%,

dec. = 120–125 °C. IR: CH₃NH₂

m(NH) 3260 m, m(C–H) 2960 m,

d(NH) 1560 m, d(CH₃) 1410s. NMR: ¹H: pm H₂9.622s, H₆

9.274ddd, ³J(H₆–H₅) = 5.7, ⁴J(H₆–H₄) = 2.1, ⁴J(H₆–H₂) = 1.2, H₄

8.898dd, ³J(H₄–H₅) = 6.9, H₅7.706ddd, ⁵J(H₅–H₂) = 1.2. MeNH₂NH

4.577s, Me 2.487t, ³J(HC–NH) = 6.6. ¹³C: pm C₂161.93, C₆161.37,

C₄159.22, C₅124.13, MeNH₂Me 33.28.

m

(NH) 3194m, m(C–H) 3000m, d(NH) 1551s, d(CH₃) 1402s. Cis iso-

mer: NMR: ¹H: pm H₂9.705s, H₆9.336ddd, ³J(H₆–H₅) = 6, ⁴J(H₆–

H₄) = 2.1, ⁴J(H₆–H₂) = 1.2, H₄8.891dd, ³J(H₄–H₅) = 7.2, H₅

7.706ddd, ⁵J(H₅–H₂) = 0.9. Me₂NH NH 4.465s, H1 2.628d ³J(H1–

NH) = 6. ¹³C: pm C₂161.47, C₆160.62, C₄159.57, C₅124.10. Me₂NH

C1 45.24.

2.1.1.3. Pt(EtNH₂)(pm)I₂. A 30% cis and 70% trans mixture was ob-

tained after 57 days of reaction. Yield = 82%, color change 155 °C,

dec. = 170–190 °C. IR: pm (20a) 3084w, (2) 3061w, (7b, 13)

3045w, (8b) 1588s, (8a) 1554w, (19b) 1465m, (19a) 1402s, (3)

1224w, (15) 1173w, (9a) 1128w, (18b) 1086w, (12) 1056w, (1)

1024w, (10b) 821w, (4) 699s, (6a) 680m, (6b) 642m. EtNH₂

2.1.1.8. Trans-Pt(Et₂NH)(pm)I₂. Reaction time 15 days, yield = 73%,

color change 110 °C, dec. = 130–145 °C. IR: Et₂NH

m(NH) 3178m,

3159m, (C–H) 2970m, 2924w, 2879w, d(NH) 1554m, d(CH₃)

m

(NH) 3206m,

m(C–H) 2990m, d(NH) 1555m, d(CH₃) 1465m,

1380m, 1374m, 1365w, other 447m. NMR: ¹H: pm H₂9.513s, H₆

9.159ddd, ³J(H₆–H₅) = 5.7, ⁴J(H₆–H₄) = 2.1, ⁴J(H₆–H₂) = 0.9, H₄

8.806dd, ³J(H₄–H₅) = 6.9, H₅7.610ddd, ⁵J(H₅–H₂) = 1.5. Et₂NH NH

4.584s, H1 3.306tq, ³J(H–H) = 6.9 and 7.2, H2 1.487t, ³J(H2–

H1) = 7.2. ¹³C: pm C₂163.79, C₆163.08, C₄158.65, C₅123.29. Et₂NH

C1 50.48, C2 14.68.

1402m. Cis isomer: NMR: ¹H: pm H₂9.704s, H₆9.338ddd, ³J(H₆–

H₅) = 6.0, ⁴J(H₆–H₄) = 2.0, ⁴J(H₆–H₂) = 1.2, H₄8.917dd, ³J(H₄–

H₅) = 7.2, H₅7.707ddd, ⁵J(H₅–H₂) = 1.5. EtNH₂NH 4.630s, H1

2.986tq, H2 1.279t, ³J(¹H2–¹H1) = 7.5. ¹³C: pm C₂161.63, C₆

160.68, C₄159.56, C₅123.69. EtNH₂C1 44.24, C2 16.82.

2.1.1.4.

Trans-Pt(nPrNH₂)(pm)I₂. Reaction

time:

(NH) 3209 m, m

65 days,

(C–H)

2.1.1.9. Pt(cprNH₂)(pm)I₂. A 80% cis and 20% trans mixture was ob-

tained after 9 days of reaction. Yield = 95%, dec. = 135–190 °C. IR:

pm (20a) 3086w, (2) 3057w, (7b, 13) 3023w, (8b) 1588s, (8a)

1552s, (19b) 1465s, (19a) 1402s, (3) 1220w, (15) 1174w, (9a)

1129m, (18b) 1086m, (12) 1054m, (1) 1024m, (10b) 820s, (4)

yield = 58%, dec. = 158–170 °C. IR: nPrNH₂

m

3026w, 3004w, d(NH) 1576w, 1554m, d(CH₃) 1467m, 1405m.

NMR: ¹H: pm H₂9.648s, H₆9.289ddd, ³J(H₆–H₅) = 6.0, ⁴J(H₆–

H₄) = 2.1, ⁴J(H₆–H₂) = 1.2, H₄8.884dd, ³J(H₄–H₅) = 6.9, H₅

7.700ddd, ⁵J(H₅–H₂) = 1.2. nPrNH₂NH 3.916s, H1 2.839m, H2

1.647m, ³J(H–H) = 6.9 and 7.5, H3 0.910t, ³J(H3–H2) = 7.2. ¹³C:

pm C₂163.85, C₆163.20, C₄159.32, C₅123.55. nPrNH₂C1 50.49,

C2 25.00, C3 11.24.

702w, (6a) 681m, (6b) 642s. cprNH₂

m(NH) 3198 m, m(C–H)

3022w, 3000w, d(NH) 1552m, d(CH) 1465m, 1402m. Cis isomer:

NMR: ¹H: pm H₂9.670s, H₆9.299ddd, ³J(H₆–H₅) = 6, ⁴J(H₆–

H₄) = 2.1, ⁴J(H₆–H₂) = 1.2, H₄8.883dd, ³J(H₄–H₅) = 7.2, H₅

7.671ddd, ⁵J(H₅–H₂) = 0.9. cprNH₂NH 4.725s, H1 3.675m, H2a

0.813m, H2b 0.709m.

2.1.1.5. Trans-Pt(nBuNH₂)(pm)I₂and trans,trans-I₂(nBuNH₂)Pt(l-

pm)Pt(nBuNH₂)I₂. In the same experimental conditions, this amine

behaved differently since the mixture contained ꢁ30% of the trans

monomer and ꢁ70 of the pyrimidine-bridged dimer after 21 days

of reaction. Total yield = 77%, color change 155 °C, dec. = 170–

180 °C. IR: pm (20a) 3085w, (2) 3070w, (7b, 13) 3024s, (8b)

1580s, (8a) 1554s, (19b) 1461s, (19a) 1406s, (3) 1211w, (15)

1185w, (9a) 1139w, (18b) 1104w, (12) 1088w, (1) 1027m, (10b)

2.1.1.10. Pt(cbNH₂)(pm)I₂. A 75% cis and 25% trans mixture was ob-

tained after 13 days of reaction. Yield = 47%, color change 150 °C,

dec. = 170–185 °C. IR: pm (20a) 3085w, (2) 3061w, (7b, 13)

3024w, (8b) 1590s, (8a) 1551m, (19b) 1465s, (19a) 1403s, (3)

1232w, (15) 1174w, (9a) 1151w, (18b) 1086m, (12) 1055w, (1)

1024w, (10b) 822s, (4) 703s, (6b) 642s. cbNH₂

m(NH) 3239w,

818m, (4) 703m, (6a) 682s, (6b) 643w. nBuNH₂

m

(NH) 3230w,

(C–H) 2958m, 2923m, 2871w, d(NH) 1554w, d(CH₃)

(Pt–N) 502w, 470w. Trans-Pt(nBuNH₂)(pm)I₂: NMR: ¹H:

3200w, (C–H) 3023w, 3000w, 2977w, d(NH) 1551m, d(CH)

m

3200 m,

1343w,

m

1465s, 1444s, 1403 m. Cis isomer: NMR: ¹H: pm H₂9.669s, H₆

9.298ddd, ³J(H₆–H₅) = 6, ⁴J(H₆–H₄) = 2.1, ⁴J(H₆–H₂) = 1.2, H₄

8.881dd, ³J(H₄–H₅) = 7.2, H₅7.668ddd, ⁵J(H₅–H₂) = 1.5. cbNH₂NH

4.130s, H1 3.672 m, J(H–H) = 7.8, H2a hidden by water of the sol-

vent, H2b 2.012m, H3ab 1.570m. ¹³C: pm C₂161.58, C₆160.73,

C₄159.67, C₅124.22. cbNH₂C1 53.90, C2 31.95, C3 14.28.

pm H₂9.652s H₆9.283dd, ³J(H₆–H₅) = 5.7, ⁴J(H₆–H₄) = 2.0, H₄

8.884dd, ³J(H₄–H₅) = 6.9, H₅7.712ddd, ⁵J(H₅–H₂) = 1.2. nBuNH₂

NH 3.910s, H1 2.923 m ³J(H–H) = 7.2, H2 1.621 m ³J(H–H) = 7.5,

H3 1.336 m ³J(H–H) = 8.1, H4 0.863t ³J(H4–H3) = 7.5. ¹³C: pm C₂

163.82, C₆163.19, C₄159.31, C₅123.53. nBuNH₂C1 49.29,

C2 33.68, C3 20.32, C4 13.93. Trans,trans-I₂(nBuNH₂)Pt(

l

-

2.1.1.11. Trans-Pt(cpNH2)(pm)I₂. Yield = 61%, color change 155 °C,

pm)Pt(nBuNH₂)I₂: NMR: ¹H: pm H₂10.090s, H_6,49.340dd,

³J(H_6,4–H₅) = 5.7, ⁴J(H_6,4–H₂) = 0.9, H₅7.650td, ⁵J(H₅–H₂) = 1.2.

nBuNH₂NH 4.530s, ²J(Pt–¹HN) = 75, H1 2.920 m ³J(H–H) = 7.2, H2

1.720 m ³J(H–H) = 7.2 and 7.5, H3 1.430 m ³J(H–H) = 7.2 and 8.1,

H4 0.940t ³J(H4–H3) = 7.5. ¹³C: pm C₂168.47, C_6,4163.76, C₅

123.67. nBuNH₂C1 49.29, C2 33.68, ³J(Pt–C2) = 30, C3 20.32, C4

13.93.

dec. = 165–190 °C. IR: cpNH₂m(NH) 3241w, 3203w, m(C–H)

3004w, 2957w, d(NH) 1554 m, d(CH) 1468s, 1405m. NMR: ¹H:

pm H₂9.649s, H₆9.290ddd, ³J(H₆–H₅) = 6, ⁴J(H₆–H₄) = 2.1, ⁴J(H₆–

H₂) = 1.2, H₄8.885dd, ³J(H₄–H₅) = 6.9, H₅7.707ddd, ⁵J(H₅–

H₂) = 1.2. cpNH₂NH 3.965s, H1 3.640 m, J(H–H) = 6.6 and 6.9,

H2a 1.958m, H2b 1.757m, H3ab 1.550m. ¹³C: pm C₂163.86, C₆

163.21, C₄158.32, C₅123.56. cpNH₂C1 60.82, C2 34.55, C3 23.99.

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F.D. Rochon, H. Titouna / Inorganica Chimica Acta 363 (2010) 1679–1693

2.1.1.12. Trans-Pt(chNH₂)(pm)I₂. Yield = 72%, color change 150 °C,

dec. = 170–185 °C. IR: chNH₂(NH) 3268w, 3235w, (C–H)

3054w, 3025w, 2976w, d(NH) 1576w, 1554 m, d(CH) 1466 m.

NMR ¹H: pm H₂9.612s, H₆9.253ddd, ³J(H₆–H₅) = 5.7, ⁴J(H₆–

H₄) = 2, ⁴J(H₆–H₂) = 1.2, H₄8.849dd, ³J(H₄–H₅) = 6.9, H₅7.670ddd

⁵J(H₅–H₂) = 1.2. cbNH₂NH 4.115s, H1 3.653m, ³J(H–H) = 6.3 and

6.7, H2a hidden by the solvent, H2b 1.903m, H3ab 1.543m. ¹³C:

pm C₂163.85, C₆163.21, C₄159.33, C₅123.55. cbNH₂C1 53.93,

C2 31.93, C3 14.28.

m

3026w, 2935w, 2852w, d(NH) 1570 m, 1554 m, d(CH) 1448 m.

NMR: ¹H: pm H₂9.649s, H₆9.290ddd, ³J(H₆–H₅) = 6, ⁴J(H₆–

H₄) = 2.1, ⁴J(H₆–H₂) = 1.2, H₄8.886dd, ³J(H₄–H₅) = 6.9, H₅

7.707ddd, ⁵J(H₅–H₂) = 1.2. chNH₂NH 4.870s, H1 3.047 m, H2a

2.500m, H2b 1.748m, H3ab 1.460m, H4 1.230m. ¹³C: pm C₂

163.87, C₆163.21, C₄159.32, C₅123.55. chNH₂C1 58.13, C2

35.43, C3 26.08, C4 25.48.

2.2. Synthesis and characterization of the chloro complexes

2.1.2. Trans-Pt(amine)(pm)I₂(amine = NH₃, MeNH₂, EtNH₂, Me₂NH,

cprNH₂and cbNH₂)

The K[Pt(tBuNH₂)Cl₃] complex was synthesized according to the

published method [20], while K[Pt(MeNH₂)Cl₃] was prepared as

described earlier [21].

The complexes trans-Pt(amine)(pm)I₂were prepared from the

isomerization of the cis compounds or the cis–trans mixture in ace-

tone at room temperature. The reaction time varied between 2 to

8 days (see below). The MeNH₂did not isomerize completely

(maximum 60% trans).

2.2.1. Pt(amine)(pm)Cl₂(amine = MeNH₂and tBuNH₂)

The compound K[Pt(amine)Cl₃] (124 mg for tBuNH₂and 156 mg

for MeNH₂) was dissolved in 3–4 mL of water. Pyrimidine (26.4 mg

for tBuNH₂or 40 mg for MeNH₂) dissolved in 3–4 mL H₂O was very

slowly added to the Pt(II) solution, which was stirred until the yel-

low color of the solution disappeared. The yellow precipitate was

ﬁltered (after 2 days for tBuNH₂and 16 h for MeNH₂), washed with

water, dried, washed with diethylether and ﬁnally dried in vacuum

in a desiccator.

2.1.2.1. Trans-Pt(NH₃)(pm)I₂. Isomerization time: 8 days, color

change 155 °C, dec. 180–220 °C. IR: NH₃

m(NH) 3297w, 3260w,

d(NH) 1551 m, 1534f. NMR: ¹H: pm H₂9.649s, H₆9.291ddd,

³J(H₆–H₅) = 6, ⁴J(H₆–H₄) = 2.1, ⁴J(H₆–H₂) = 0.9, H₄8.887dd, ³J(H₄–

H₅) = 6.9, H₅7.705ddd, ⁵J(H₅–H₂) = 1.2. NH₃3.925s. ¹³C: pm C₂

163.97, C₆163.28, C₄159.32, C₅123.53.

2.2.1.1. Trans-Pt(tBuNH₂)(pm)Cl₂. Yield 73%, color change 200 °C,

dec. = 220–270 °C. IR: pm (20a) 3125m, (2) 3102w, (7b, 13)

3072m, (8b) 1583s, (8a) 1559m, (19b) 1474m, (19a) 1411s, (3)

1300s, (15) 1201w, (9a) 1137w, (18b) 1087w, (12) 1060w, (1)

1031w, (10b) 822s, (4) 752w, (6a) 682s, (6b) 648w. tBuNH₂

2.1.2.2. Pt(MeNH₂)(pm)I₂. The trans isomer was obtained in a pro-

portion of 60% after 8 days and the mixture started to decompose.

IR of mixture: IR: pm (20a) 3087w, (2) 3061w, (7b, 13) 3040s, (8b)

1578w, (8a) 1540s, (19b) 1455m, (15) 1175w, (9a) 1129w, (18b)

1068w, (12) 1056m, (1) 1000m, (10b) 826w, (4) 698m, (6a)

m(NH) 3200s,

m

(C–H) 2980m, d(NH) 1580–1594m, d(CH₃) 1399–

680m, (6b) 650m. MeNH₂

m(NH) 3260m,

m(C–H) 2965m, d(NH)

1372m, (Pt–N) 420w, 462w, m

m

(Pt–Cl) 338s. NMR: ¹H: pm H₂

1560m, d(CH₃) 1420s. Trans isomer: NMR: ¹H: pm H₂9.460s, H₆

9.121ddd, ³J(H₆–H₅) = 5.7, ⁴J(H₆–H₄) = 2.1, ⁴J(H₆–H₂) = 0.9, H₄

8.781dd, ³J(H₄–H₅) = 6.9, H₅7.565ddd, ⁵J(H₅–H₂) = 1.5. MeNH₂NH

4.437s, H1 2.545t, ³J(H1–HN) = 6.3. ¹³C: pm C₂163.86, C₆163.13,

C₄158.66, C₅123.28. MeNH₂C1 35.18.

9.448s, H₆9.095ddd, ³J(H₆–H₅) = 5.7, ⁴J(H₆–H₄) = 2.1, ⁴J(H₆–

H₂) = 1.2, H₄8.896dd, ³J(H₄–H₅) = 4.8, H₅7.615ddd, ⁵J(H₅–

H₂) = 1.2. tBuNH₂NH 4.489s, CH₃1.417s. ¹³C: pm C₂161.38, C₆

160.46, C₄158.90, C₅122.83. tBuNH₂C1 55.81, C2 30.81.

2.2.1.2. Pt(MeNH₂)(pm)Cl₂. The isolated product contained ꢁ25% cis

and ꢁ75% trans. Total yield 51%, color change 190 °C, m. p. = 230 °C.

IR: pm (20a) 3105w, (2) 3076w, (8b) 1596s, (8a) 1559m, (19b)

1499m, (19a) 1414m, (3) 1326s, (15) 1179w, (9a) 1137w, (18b)

1092w, (12) 1069w, (1) 1026w, (10b) 825s, (6a) 700s, (6b) 647s.

2.1.2.3. Trans-Pt(EtNH₂)(pm)I₂. Isomerization time: 2 days, color

change 160 °C, dec. = 175–190 °C. IR: EtNH₂

m

(NH) 3204w,

3114w,

m

(C–H) 2923w, d(NH) 1554 m, d(CH₃) 1466 m. NMR: ¹H:

pm H₂9.648s, H₆9.289ddd, ³J(H₆–H₅) = 6, ⁴J(H₆–H₄) = 2.1, ⁴J(H₆–

H₂) = 1.2, H₄8.888dd, ³J(H₄–H₅) = 6.9, H₅7.706ddd, ⁵J(H₅–

H₂) = 1.5. EtNH₂NH 4.438s, H1 2.902 m (partially hidden by

water), H2 1.277t, J(H2–H1) = 7.5. ¹³C: pm C₂163.97, C₆163.28,

C₄159.32, C₅123.55. EtNH₂C1 42.99, C2 14.68.

MeNH₂

m

(NH) 3194w,

m

(C–H) 2950m, d(NH) 1559m, d(CH₃)

(Pt–Cl) 353, 350, 347s. Cis isomer:

1451m, 1414s,

m

(Pt–N) 445m,

m

NMR: ¹H: pm H₂9.810s, H₆9.386ddd, ³J(H₆–H₅) = 6.3, ⁴J(H₆–

H₄) = 2.1, ⁴J(H₆–H₂) = 1.5, H₄9.215dd, ³J(H₄–H₅) = 6.9, H₅

8.030ddd, ⁵J(H₅–H₂) = 0.9. MeNH₂NH 6.737s, H1 2.663t, ³J(H1–

NH) = 6.3.

2.1.2.4. Trans-Pt(Me₂NH)(pm)I₂. Isomerization time: 8 days, color

change 150 °C, dec. = 160–175 °C. IR: Me₂NH

m

(NH) 3209w,

3244w,

m

(C–H) 2958w, 2923s, d(NH) 1554s, d(CH₃) 1405s. NMR:

2.2.1.3. Trans-Pt(MeNH₂)(pm)Cl₂. The trans isomer was obtained

pure after isomerization of the mixture in acetone at room temper-

ature during 48 h. m. p. = 210–230 °C. IR: pm (20a) 3117w, (2)

3091w, (7b, 13) 3065w, (8b) 1599s, (8a) 1562 m, (19b) 1470m,

(19a) 1417s, (3) 1228m, (15) 1178w, (9a) 1142w, (18b) 1088w,

(12) 1067w, (1) 1018w, (10b) 807w, (4) 703m, (6a) 690s, (6b)

¹H: pm H₂9.648s, H₆9.289ddd, ³J(H₆–H₅) = 5.7, ⁴J(H₆–H₄) = 2.1,

⁴J(H₆–H₂) = 1.2, H₄8.884dd, ³J(H₄–H₅) = 6.9, H₅7.706ddd, ⁵J(H₅–

H₂) = 1.5. Me₂NH NH 4.280s, H1 hidden by water of the solvent.

¹³C: pm C₂163.49, C₆162.85, C₄158.98, C₅123.22. Me₂NH C1

43.37.

651s. MeNH₂

1446w, 1417s,

m

(NH) 3221w,

m

(C–H) 2942w, d(NH) 1557m, d(CH₃)

2.1.2.5. Trans-Pt(cprNH₂)(pm)I₂. Isomerization time: 3 days,

m(Pt–N) 502w, 450w, m

(Pt–Cl) 353s. NMR: ¹H: H₂

dec. = 150–190 °C. IR: cprNH₂

m

(NH) 3254m,

m

(C–H) 2923w,

9.692s, H₆9.344ddd, ³J(H₆–H₅) = 6, ⁴J(H₆–H₄) = 2.1, ⁴J(H₆–

H₂) = 1.2, H₄9.164dd, ³J(H₄–H₅) = 6.9, H₅7.976ddd, ⁵J(H₅–

H₂) = 1.2. MeNH₂NH 6.580s, H1 2.607s. ¹³C: pm C₂162.22, C₆

160.77, C₄160.18, C₅123.95. MeNH₂C1 34.60.

2852w, d(NH) 1560w, d(CH) 1460 m. NMR: ¹H: pm H₂9.614s, H₆

9.255ddd, ³J(H₆–H₅) = 6, ⁴J(H₆–H₄) = 2.1, ⁴J(H₆–H₂) = 1.2, H₄

8.851dd, ³J(H₄–H₅) = 7.2, H₅7.665ddd, ⁵J(H₅–H₂) = 0.9. cprNH₂

NH 4.550s, H1 3.653 m, J(H–H) = 6.3 and 6.9, H2a 0.805m, H2b

0.701m. ¹³C: pm C₂163.87, C₆163.19, C₄159.26, C₅123.48. cprNH₂

C1 hidden by the solvent, C2 8.03.

2.2.2. Cl2(amine)Pt(l-pm)Pt(amine)Cl2 (amine = MeNH2 and

tBuNH2)

The complex K[Pt(amine)Cl₃] (106 mg) is dissolved in 4 mL of

water. Pyrimidine is dissolved in 3 mL of water and is slowly added

to the Pt(II) solution. The Pt:pm ratio of 2.1:1 must be respected to

2.1.2.6.

Trans-Pt(cbNH₂)(pm)I₂. Isomerization

time:

5 days,

dec. = 175 ꢀ180 °C. IR: cbNH₂

m

(NH) 3239w, 3201w, m(C–H)

F.D. Rochon, H. Titouna / Inorganica Chimica Acta 363 (2010) 1679–1693

1683

prevent the formation of monomers. The mixture is stirred during

one week for tBuNH₂and 24 h for MeNH₂. The yellow precipitate is

ﬁltered, washed with water, dried in air, washed with diethylether

and ﬁnally dried in vacuum in a desiccator.

trans mixtures. Only one cis compound (MeNH₂) could be isolated

pure. A few amines, especially the more bulky ones produced only

trans isomers.

The products containing cis compounds were isomerized in ace-

tone at room temperature to obtain pure trans isomers, except for

the MeNH₂complex, which started to decompose after 8 days in

acetone. The mixture contained a maximum of 60% of trans

isomers.

2.2.2.1. Trans,trans-Cl₂(tBuNH₂)Pt(l-pm)Pt(tBuNH₂)Cl₂. Yield = 74%,

dec. = 225–260 °C. IR: pm (20a) 3125 m, (2) 3080w, (8b) 1601s,

(8a) 1583s, (19b) 1463 m, (19a) 1412 m, (3) 1300s, (15) 1200s,

(9a) 1137w, (18b) 1087m, (12) 1030w, (1) 928w, (10b) 822s, (4)

The ligand nBuNH₂behaved quite differently. In the same

experimental conditions, this amine produced after 21 days of

reaction a mixture which contained ꢁ20% of trans-Pt(nBuNH₂)(p-

747w, (6a) 682s, (6b) 633w. tBuNH₂

m(NH) 3225–3200s,

m(C–H)

2968m, d(NH) 1601m, d(CH₃) 1399 m, 1373 m,

m

(Pt–N) 502w,

m)I₂and ꢁ80% of the pyrimidine-bridged dimer I₂(nBuNH₂)Pt(

l-

460w, 422w,

m

(Pt–Cl) 342s. NMR: ¹H: pm H₂10.040s, H_6,4

pm)Pt(nBuNH₂)I₂. A few preliminary experiments were done with

9.377dd, ³J(H_6,4–H₅) = 6.9, ⁴J(H_6,4–H₂) = 0.9, H₅7.700td, ⁵J(H₅–

H₂) = 1.5. tBuNH₂NH 4.654s, CH₃1.453s. ¹³C: pm C₂164.45, C_6,4

161.85, C₅123.72. tBuNH₂C1 56.00, C2 31.00. d(Pt) = ꢀ2128 ppm.

other amines in order to obtain such dimers, but without success.

3.1.1.2. IR spectroscopy. The IR spectrum of free pyrimidine (C_2v

)

was published [19,22–24]. There are 22 vibration modes (A₁, B₁

and B₂) which are active in IR, while the two A₂modes are active

only in Raman spectroscopy. When the molecule is coordinated

to a metal, its symmetry is reduced to C_sand all the 24 vibration

modes are active in IR [19]. There is no theoretical IR study in

the literature on Pt–pyrimidine complexes, but we have published

recently a few results on Pt(Ypy)(pm)Cl [10] and trans,trans-Cl₂(Y-

2.2.2.2. Trans,trans-Cl₂(MeNH₂)Pt(l-pm)Pt(MeNH₂)Cl₂. Yield = 61%,

color change 170 °C, m. p. 200 °C. IR: pm (20a) 3121w, (2)

3059w, (8b) 1604s, (8a) 1575m, (19b) 1461m, (19a) 1412m, (3)

1270w, (15) 1186w, (9a) 1138w, (18b) 1087s, (12) 1046m, (1)

991m, (10b) 810s, (4) 729w, (6a) 689s, (6b) 677s. MeNH₂

3263, 3235, 3202 m, (C–H) 2942w, d(NH) 1604s, d(CH₃) 1411s,

1356w, (Pt–N) 520, 503, 495w,

(Pt–Cl) 328s. NMR: ¹H: H₂

m(NH)

m

py)Pt(l-pm)Pt(Ypy)Cl₂[10], where we proposed an assignment

m

10.030s, H_6,49.360dd, ³J(H_6,4–H₅) = 5.7, ⁴J(H_6,4–H₂) = 0.9, H₅

7.774td, ⁵J(H₅–H₂) = 1.5. MeNH₂NH 4.662s, H1 2.489t, J(H1–

HN) = 6.5. ¹³C: pm C₂164.39, C_6,4161.94, C₅123.96. MeNH₂C1

34.07. d(Pt) = ꢀ2152 ppm.

based on the published works on free pyrimidine.

The IR spectra of the pure compounds cis-Pt(MeNH₂)(pm)I₂and

trans-Pt(amine)(pm)I₂were recorded and a tentative assignment

of bonded pyrimidine is shown in Table 1. In these complexes,

the energies of the vibrations are quite similar to those of the free

molecule.

3. Results and discussion

Several of these vibrations (20a, 2, 7b and 13) are mainly

stretching aromatic

3000 cm^ꢀ1. In the 1600–1400 cm^ꢀ1region, the stretching

and (C–N) modes (8a, 8b, 19a, 19b) coupled to deformation d(C–

m

(C–H) vibrations between 3090 and

3.1. The iodo complexes

m(C–C)

m

Compounds of the type Pt(amine)(pm)I₂containing ami-

ne = NH₃, several primary aliphatic and cyclic amines and two sec-

ondary amines were synthesized and characterized. In the same

experimental conditions, the reaction with n-butylamine produced

also a pyrimidine-bridged dimer, which will discussed in a differ-

ent section.

H) modes are strong bands. The deformation modes in the hetero-

cyclic plane (9a, 12, 18a and 1) were assigned in the region 1185–

990 cm^ꢀ1. Mode 1 is the vibration of the complete aromatic ring,

10b the umbrella mode, 4 the intense out of plane vibration mode

and ﬁnally the 6a and 6b modes are out of plane deformations. We

have also measured the IR spectra of the mixtures cis- and trans-

Pt(am)(pm)I₂where am = NH₃, MeNH₂, EtNH₂, Me₂NH, cprNH₂et

cbNH₂. The observed bands are shown in the experimental section.

The amine bands are shown in the experimental section. The N–

H stretching and deformation modes were observed at 3360–3320

and 1630–1580 cm^ꢀ1, respectively in the free amines, but at lower

3.1.1. Pt(amine)(pm)I₂

3.1.1.1. Synthesis. The complexes Pt(amine)(pm)I₂were synthe-

sized from the reaction of the diiodo-bridged dimer I(ami-

ne)Pt(l-I)₂Pt(amine)I in suspension in water. The latter were

energies in the Pt(II) complexes (3297–3114 and 1576–1551 cm^ꢀ1

respectively) as expected.

,

prepared from the reaction of Pt(amine)₂I₂with perchloric acid.

The formation of the diiodo-bridged dimers is very slow, since

the two compounds are quite insoluble. It is important to let the

reaction continue for a long time, since the presence of Pt(ami-

ne)₂I₂in the dimer will be carried on in the subsequent procedures.

The cleavage of the diiodo-bridged dimers is performed with a

slight excess of pyrimidine. Since the trans effect of iodo ligands

is larger than the one of amines, cis isomers are obtained from

the trans diido-bridged dimer. Cis and trans dimers are known to

exist in solution [18], but the concentration of the trans dimers is

slightly larger. The cleavage of the cis dimers should produce one

cis molecule and one trans molecules of Pt(amine)(pm)I₂, although

the cleavage of the cis dimers should be slower than the cleavage of

the trans dimers (because of the trans effect).

IR spectroscopy is often a good method to determine the geom-

etry of compounds of the type PtN₂X₂. Two stretching (Pt–X) and

(Pt–N) bands (A₁+ B₁, C_2vskeleton symmetry) are expected for

m

the cis compounds, while only one band (B_3u, D_2hskeleton symme-

try) should be observed for the trans isomers. When the two N-li-

gands are different, the symmetry is lowered, but often the same

observations have been reported. The

served at frequencies <260 cm^ꢀ1and could not be measured on

our instrument. The assignment of the (Pt–N) modes are more dif-

m(Pt–I) vibrations are ob-

m

ﬁcult, since they are weak bands, which can couple with other

vibrations. In the literature, they have been assigned in different

regions. For most of the amine complexes, they were assigned

around 500 cm^ꢀ1. But for a few compounds like cis- and trans-

Pt(pyrazine)₂X₂[25] and a few other complexes containing pyri-

O

IðamineÞPtð

l

-IÞ₂PtðamineÞIÞ þ 2 pm ^H!²2PtðamineÞðpmÞI₂

dine derivatives [26], they were assigned to bands <300 cm^ꢀ1

.

Therefore cis or a cis–trans Pt(amine)(pm)I₂mixture was ex-

pected. With bulky amines, isomerisation of the cis mixed-ligands

complexes will occur even in water. The IR and NMR characteriza-

tion of the products has shown that most compounds were cis and

The latter energies seem very small for stretching

could correspond to deformation modes. We have chosen to assign

the (Pt–N) stretching bands in our compounds to the region

around 500 cm^ꢀ1, based on several reported studies on Pt(II) com-

m(Pt–N) and they

m

1684

F.D. Rochon, H. Titouna / Inorganica Chimica Acta 363 (2010) 1679–1693

plexes containing amines, pyridine derivatives, pyrimidine and

pyrazine [10,27–32]. All our complexes have shown vibrations in

partial multiple bond between pm and Pt. The back-donation of

*

p molecular orbital

electron density from the Pt atom to an empty

this region, which could correspond to

are shown in Table 2. The IR spectra of the cis–trans mixtures have

shown the presence of four bands between 438 and 503 cm^ꢀ1

m

(Pt–N) bands and they

on pm would reduce the electron density of the Pt atom, thus

would cause a deshielding effect in ¹⁹⁵Pt NMR. Therefore the differ-

ence in the resonance observed in the two types of compounds

.

After the isomerisation of the mixture, two bands were observed

at 472 and 502 cm^ꢀ1for the pure trans compounds. The two other

bands observed in the mixture could correspond to the cis isomer.

The pure cis MeNH₂complex showed also two bands in this region.

Since the two N-ligands are very different, the squeleton PtN₂I₂

symmetry is not a good approximation in this type of compound.

could indicate the presence of p-bonding in the Pt–pm bond. These

results indicate that multinuclear magnetic resonance spectros-

copy might be a good technique to study the nature of the Pt-

pyrimidine bond.

In order to study the inﬂuence of the basicity of the amines on

the ¹⁹⁵Pt chemical shifts, the d(¹⁹⁵Pt) values were compared to the

pKa values of the amines [34–35]. There is no relation, since all the

values are almost identical except for the MeNH₂complexes,

which were observed at slightly higher ﬁelds. The pKa values are

measured in a solvent different from acetone and the difference

due to the basicity of the amine is probably a small factor in these

¹⁹⁵Pt NMR data. The proton afﬁnities are usually a better indicator

for the basicity of a molecule, since it is measured in the gas phase,

but there are not many data available in the literature. For our

complexes, there are no correlation between the observed

d(¹⁹⁵Pt) with the published proton afﬁnities of the amines [36,37].

3.1.1.3. ¹⁹⁵Pt NMR spectroscopy. There are only four papers in the

literature on ¹⁹⁵Pt NMR of Pt–pm compounds. These are on the

complexes cis and trans-Pt(R₂SO)(pm)Cl₂[14], cis and trans-Pt(Y-

py)(pm)Cl₂[10], trans-Pt(R₂SO)(pm)I₂[15] and the pyrimidine-

bridged dimers K₂[Cl₃Pt(

l

-pm)PtCl₃] and Cl₂(R₂SO)Pt(

l-

pm)Pt(R₂SO)Cl₂[9] and Cl₂(Ypy)Pt(l-pm)Pt(Ypy)Cl₂[10].

The ¹⁹⁵Pt NMR spectra of all the new compounds Pt(amine)(p-

m)I₂were measured in CD₃COCD₃. Their chemical shifts d(¹⁹⁵Pt)

are shown in Table 3. For the cis compounds, only the MeNH₂com-

plex was pure. The others were either cis–trans mixtures or pure

trans compounds. All the isomerized products were pure trans

compounds, except the MeNH₂complex which still contained

40% of the cis isomers. A few compounds contained small quanti-

ties of the starting material Pt(amine)₂I₂, which could be identiﬁed

from the literature [28,32].

3.1.1.4. 1H NMR spectroscopy. The symmetry of free pyrimidine is

C_2v. The labeling scheme of free pyrimidine is shown in Scheme 1.

The atoms C₄and C₆are equivalent as are H₄and H₆. The proton

chemical shifts are: H₂9.145, H₄,₆8.760 and H₅7.480 ppm in

CD₃COCH₃. This order can be explained by the different ionic reso-

nance structures and by the inductive effect of the two N atoms.

The latter is more important for the atoms close to the N atoms.

The two effects lower drastically the electron density on C₂and

The results on Table 3 show that the d(¹⁹⁵Pt) values are very

similar for the two isomers. For the RNH₂complexes, the difference

D

d (d(cis)- d(trans)) vary between ꢀ10 and +6 ppm, close to the

hence H₂. The

p electron densities on the C atoms are also shown

experimental errors. This is different from the results reported on

the complexes cis- and trans-Pt(Ypy)(pm)Cl₂, where the cis com-

pound was found at higher ﬁeld than the one of the corresponding

trans analog, with an average difference between the two isomers

in Scheme 1 [38].

H₅is a doublet of triplet with ³J(H₅–H_4,6) = 5.1 Hz and ⁵J(H₅–

H₂) = 1.5 Hz, H_4,6is a doublet and H₂is a singlet. The presence of

the two neighboring N atoms with strong quadrupolar magnetic

moments is responsible for the absence of couplings on H₂.

The binding of pyrimidine to Pt(II) in a monodentate fashion re-

duces its symmetry to C_sand all the H atoms are different as shown

in Scheme 2. Therefore 4 different signals are observed in ¹H NMR.

The presence of the Pt–N₁bond leads to the following deshielding

order: H₂> H₆> H₄> H₅.

of ꢀ38 ppm) [10]. For cis- and trans-Pt(amine)₂I₂[28,32], the

Dd

values vary between ꢀ10 and 22 ppm in acetone and from 16 to

38 ppm in DMF for cyclic amines. For the dichloro analogs, the

D

d values vary between 9 and 21 ppm in DMF for cyclic amines

[32]. For the secondary amine Me₂NH, the

Dd value is slightly lar-

ger (ꢀ16 ppm) (Table 3).

For primary amines, the average d(¹⁹⁵Pt) values are ꢀ3298 and

ꢀ3292 ppm for the cis- and trans-Pt(RNH₂)(pm)I₂isomers, respec-

tively. The corresponding cis- and trans-Pt(RNH₂)₂I₂compounds

were observed at slightly higher ﬁelds (average values around

ꢀ3353 and ꢀ3362 ppm, respectively) [28,33]. The substitution of

an amine ligand by a pyrimidine ligand lowers the electron density

on the metal atom, which could be caused by the formation of a

In the complexes Pt(amine)(pm)I₂, the signal of H₂is a singlet,

because of the presence of the two neighboring N atoms. The signal

of H₄is a doublet of doublets with ³J(H₄–H₅) = 6.9–7.2 Hz and

⁴J(H₄–H₆) = 1.8–2.1 Hz. H₅is a doublet of doublets of doublets with

Table 3

pKa, proton afﬁnity (PA, kJ/mol), d(¹⁹⁵Pt) and

cis- and trans-Pt(amine)(pm)I₂.

Dd (cis–trans) (ppm) of the complexes

Amine

pKa [34,35] PA [36,37] cis

trans

D

d (d_cisꢀ d_trans

)

NH₃

MeNH₂

EtNH₂

nPrNH₂

nBuNH₂

isoPrNH₂

Me₂NH

Et₂NH

cprNH₂

cbNH₂

cpNH₂

chNH₂

Ave. RNH₂

Ave. R₂NH

9.24

ꢀ3300

ꢀ3290 ꢀ10

Scheme 1.

10.62

10.67

10.708

10.777

10.63

10.732

11.04

8.67

914

930

933

924

ꢀ3329 ꢀ3326 ꢀ3

ꢀ3292 ꢀ3290 ꢀ2

ꢀ3289

ꢀ3287

ꢀ3285

ꢀ3304 ꢀ3288 ꢀ16

ꢀ3313

ꢀ3286 ꢀ3292

ꢀ3285 ꢀ3289

ꢀ3286

6

4

9.34

9.98

9.85

ꢀ

ꢀ3290

ꢀ3298 ꢀ3292

ꢀ3300

Scheme 2.

F.D. Rochon, H. Titouna / Inorganica Chimica Acta 363 (2010) 1679–1693

1685

³J(H₅–H₆) = ꢁ6.0 Hz and ⁵J(H₅–H₂) = 0.9–1.5 Hz. Finally, the signal

of H₆is also a doublet of doublets of doublets, since it couples with

H₂(J = 0.9–1.5 Hz) H₄and H₅. This coupling pattern is similar to

those observed in the complexes cis- and trans-Pt(R₂SO)(pm)Cl₂

[14] and cis- and trans-Pt(Ypy)(pm)Cl₂[10].

ally larger in the cis complexes. They are often difﬁcult to measure

since the neutral compounds are not very soluble in organic sol-

vents. Furthermore, it is more difﬁcult to observe them on a higher

ﬁeld instrument because of chemical shift anisotropy. The proton

coupling constants with ¹⁹⁵Pt could be measured for most of our

compounds and the values are shown in Table 5. The

³J(¹⁹⁵Pt–¹H₆) values are larger in the cis complexes (ave. 39 Hz)

than in the trans analogs (ave. 33 Hz). The ³J(¹⁹⁵Pt–¹H₂) values

are also larger in the cis geometry (25 Hz versus 22 Hz), although

the difference is much smaller. Similar values were observed for

cis- and trans-Pt(R₂SO)(pm)Cl₂[14], trans-Pt(R₂SO)(pm)I₂[15]

and cis- and trans-Pt(Ypy)(pm)Cl₂[10]. Therefore NMR spectros-

copy seems an excellent method to determine the geometry of

such Pt(II) compounds.

The proton NMR spectra of the free amines were measured in

the same solvent (CD₃COCD₃) and were compared to the amine li-

gands in the complexes. Three amines (MeNH₂, EtNH₂and Me₂NH)

are commercially available in water; therefore their NMR spectra

were measured in a larger quantity of water than the other com-

pounds. The chemical shifts are inﬂuenced by the quantity of water

The signals of pyrimidine have shown a downﬁeld shift upon

coordination, since the formation of the

tron density on the ligand, while it is increased on the Pt atom.

The chemical shifts differences

d (d_ligandꢀ d_{free pm}) (where the

r bond reduces the elec-

D

spectrum of free pm was measured in the same solvent) are shown

in Table 4 for the cis and trans isomers. The results are similar to

those observed for the complexes cis- and trans-Pt(R₂SO)(pm)Cl₂

[14] and trans-Pt(Ypy)(pm)Cl₂[10], but different from those re-

ported recently for cis-Pt(Ypy)(pm)Cl₂[10]. For the latter com-

pounds, the signal of H₂does not follow the expected pattern,

since a much larger downﬁeld shift is observed for H₆(ave.

D

d = 0.753 ppm), while the position of H₂is almost not affected

by coordination. The assignments in the cis- and trans-Pt(Y-

py)(pm)Cl₂isomers were conﬁrmed by 2D ¹H NMR studies [10].

The signals of H₂and H₆in our compounds are deshielded by

ꢁ0.5 ppm, while those of H₄and H₅are less affected. For the com-

in acetone. Therefore it is difﬁcult to compare the

D

d (d_ligandꢀ d_free

plexes cis- and trans-Pt(R₂SO)(pm)Cl₂[14] the ave.

D

d values are

_amine) values of these three amines with the others. For the cyclic

amines, the geminal protons on each –CH₂group are not equiva-

lent, since one H atom is on the same side as the N atom, while

the second is on the opposite side. The proton on the same side

as the N atom is more deshielded in ¹H NMR than the other one.

The difference is more important for the closer –CH₂groups.

H₂= 0.217, H₆= 0.255 ppm (cis), and H₂= 0.304, H₆= 0.313 ppm

(trans) in CD₂Cl₂, except for cis-Pt(dibenzylsulfoxide)(pm)Cl₂,

where all the signals were observed at higher ﬁeld than in free

pyrimidine. In the ionic compound cis-[Pt(NH₃)₂(pm)₂](ClO₄)₂,

the

The average

shown in Table 4. The signals of the pyrimidine ligand are more

deshielded in the cis complexes. For each amine, the average

D

d values are: H₂= 0.45 ppm and H₆= 0.36 ppm in D₂O [11].

D

d values for the cis and trans compounds are also

The proton chemical shifts of the amine ligands and the Dd val-

ues are listed in Table 6. All the NH signals are shifted towards low-

er ﬁeld upon coordination, except for the cpNH₂complex. It is

difﬁcult to compare the signals of the different amine ligands. Fur-

thermore, the acetone and water signals sometimes interfere with

the amine signals. We can compare the results on the two isomers,

but we do not have many data in order to make a good comparison.

There are two aliphatic primary amines (MeNH₂and EtNH₂), two

cyclic primary amines (cprNH₂and cbNH₂), NH₃a ligand which

is different from the other amines and a secondary amine Me₂NH,

where the –CH₃signal of the trans isomer is lost in the water sig-

D

d

value is larger for the cis isomer. The total average for the cis com-

pound is 0.360 ppm, while it is 0.319 ppm for the trans complexes

(Table 4). The difference might be caused by the ligand located in

trans position. Iodo ligands have a larger trans effect than amines.

The difference in chemical shifts difference does not seem to be re-

lated to the size of the amine. The results on the trans isomers

show that the ave.

est amine (MeNH₂) and the most bulky one (Et₂NH). The average

chemical shift difference (ave. d) of the pm ligand is also not re-

Dd values are very similar, except for the small-

D

nal. It is therefore difﬁcult to compare these amines. The Dd

lated to the pKa of the protonated amine or to the proton afﬁnity of

the amine.

(d_cisꢀ d_trans) values of the amine group are always positive and var-

ies between 0.02 and 0.19 ppm. Therefore the NH signal of the cis

The cis or trans geometry of a Pt(II) compound can often be

compound is found at lower ﬁeld that the one in its trans isomer.

P

determined from its coupling constants J(¹⁹⁵Pt–¹H), which are usu-

The

Dd values for the other protons vary with the amines and

there is no general trend between the cis and the trans isomers.

Table 4

D

d and ave.

D

d (ppm) of pyrimidine in the complexes cis-Pt(amine)(pm)I₂

Table 5

Coupling constants ³J(¹⁹⁵Pt–¹H_2,6) (Hz) of pm in cis- et trans-Pt(amine)(pm)I₂.

Amine

H₂

H₆

H₄

H₅

Ave. Dd

Amine

NH₃

Isomer

³J(¹⁹⁵Pt–¹H₂)

³J(¹⁹⁵Pt–¹H₆)

Free pm (d)

NH₃cis

Trans

MeNH₂cis

Trans

EtNH₂cis

Trans

nPrNH₂trans

nBuNH₂trans

isoPrNH₂trans

Me₂NH cis

Trans

Et₂NH trans

cprNH₂cis

Trans

cbNH₂cis

Trans

cpNH₂trans

chNH₂trans

9.145

0.561

0.504

0.477

0.315

0.559

0.503

0.507

0.501

0.560

0.503

0.368

0.525

0.469

0.524

0.467

0.504

8.760

0.575

0.531

0.514

0.361

0.578

0.529

0.523

0.527

0.576

0.529

0.399

0.539

0.495

0.538

0.493

0.530

8.760

0.159

0.127

0.138

0.021

0.157

0.128

0.124

0.125

0.131

0.124

0.046

0.123

0.091

0.121

0.089

0.125

0.126

7.480

0.225

0.226

0.085

0.227

0.226

0.220

0.232

0.228

0.226

0.134

0.191

0.185

0.188

0.190

0.227

0.380

0.347

0.339

0.196

0.380

0.347

0.344

0.347

0.345

0.373

0.346

0.237

0.345

0.310

0.342

0.310

0.347

cis

trans

cis

trans

cis

25

22

27

22

24

23

22

23

21

25

21

20

24

21

23

22

40

36

38

33

37

31

34

31

32

40

31

32

42

35

38

33

36

MeNH₂

EtNH₂

trans

cis

trans

cis

trans

cis

trans

nPrNH₂

nBuNH₂

isoPrNH₂

Me₂NH

Et₂NH

cprNH₂

cbNH₂

cpNH₂

chNH₂

Ave.

D

d cis

d trans

0.534

0.474

0.553

0.541

0.138

0.114

0.214

0.219

0.360

0.319

Ave.

cis

trans

25

22

39

33

1686

F.D. Rochon, H. Titouna / Inorganica Chimica Acta 363 (2010) 1679–1693

Table 6

5

d(¹H),

D

d (ppm) and J(¹⁹⁵Pt–¹H) (Hz) of amine in cis- and trans-Pt(amine)(pm)I₂.

EtNH₂

Amine NH

H1

H2

H3

H4

H4ab^a

4.5

4

H2a^a

H2b^a

H3ab^a

nBuNH₂

NH₃

cis

trans

4.121

3.925

nPrNH₂

3.5

3

MeNH₂

cis

4.543

4.437

2.447 ³J = 48

ꢀ0.480

MeNH₂

D

d

trans

2.545

2.5

D

d

ꢀ0.382

910

915

920

925

930

935

EtNH₂

cis

2.986^b

0.368

1.279

0.273

1.277

0.271

PA (KJ/mole)

4.630

0.380

4.438

0.188

D

d

trans

2.902^b,c

0.284

Fig. 1. d(NH₂) vs. proton afﬁnities (PA) of the amine in trans- Pt(amine)(pm)I₂.

D

d

nPrNH₂

trans

3.916 ²J = 78 2.839

0.364 -0.261

1.647

0.102

0.910

0.028

Attemps to relate the d(H1) (H1 is in

group) values with the pKa or the proton afﬁnity of the amine were

unsuccessful. In order to gain information on the strength of the

bond (amine ? Pt) and how it can be related to changes in the

NMR spectra, we have attempted to relate the observed d values

a position to the amine

D

d

nBuNH₂

trans

3.910 ²J = 68 2.923

1.621

0.128

1.336

0.015

0.863

ꢀ0.004

r

D

d

0.329

ꢀ0.198

D

isoPrNH₂

trans

4.030

0.310

3.785

0.784

1.282

0.320

of the amine ligand with the pKa or the proton afﬁnity of the

amines, but no relation was found.

D

d

Several ²J(¹⁹⁵Pt–¹HN) couplings were observed for the trans iso-

mers. They vary from 58 to 78 Hz. It was not possible to measure

any values for the cis isomers, mainly because of the isomerisation

to the trans geometry. Two ³J(¹⁹⁵Pt–H1) couplings could be ob-

served for the cis compounds. These values are 48 Hz for the

MeNH₂compound and 32 Hz for the Me₂NH compound. These

couplings are hidden by the solvents (water and acetone) for the

equivalent trans isomers. Therefore it is not possible to compare

these values in relation to the geometry of these complexes. In

the complexes Pt(Ypy)₂Cl₂[27], Pt(amine)₂X₂[28,32],

Pt(R₂SO)(pm)Cl₂[14] and Pt(Ypy)(pm)Cl₂[10], these values are lar-

ger in the cis geometry.

Me₂NH

cis

4.465

4.280

2.628 ³J = 32

D

d

0.366

b

trans

Et₂NH

trans

4.584 ²J = 78 3.306

0.354

1.487

0.488

D

d

0.754

cprNH₂

cis

4.725

0.805

4.550

0.630

3.675

0.805

3.653

0.783

0.813

0.122

0.805

0.114

0.709

0.139

0.701

0.131

D

d

trans

D

d

cbNH₂

cis

b

4.130

0.170

3.672

0.170

2.012

0.065

1.903

ꢀ0.044 ꢀ0.168

1.570

D

d

ꢀ0.141

trans

4.115 ²J = 63 3.653

1.543

3.1.1.5. 13C NMR spectroscopy. As in ¹H NMR, four signals will be

D

d

0.155

0.151

observed in ¹³C NMR for Pt-bonded pyrimidine. The chemical shifts

cpNH₂

trans

are shown in the experimental section and the

Dd values

3.965 ²J = 65 3.640

ꢀ0.335 ꢀ0.140

1.958

0.229

1.757

0.221

1.550

0.123

(d_pmꢀ d_{free pm}) in CD₃COCD₃) are shown in Table 7. All the pm sig-

D

d

nals were observed at lower ﬁeld than those of free pyrimidine.

chNH₂

trans

4.870 ²J = 58 3.047

0.695

ꢀ0.189

2.500

ꢀ0.038 0.025

1.748

1.460

0.176

1.230

0.213

The

Dd values are largest for C₆followed closely by C₂in the two

isomers, but the values are much larger for the trans compounds

as shown in Table 7. These values are 2.02 (C₂) and 3.07 ppm

(C₆) for the cis isomers and 4.22 and 5.42 ppm, respectively for

D

d

a

b

c

Cyclic amine.

Hidden or partially hidden by water or acetone.

3.076 in CDCl₃.

the trans compounds. The overall ave.

Dd values are 2.11 ppm for

the cis compounds and 2.95 ppp for the trans analogs. Therefore

the average electron density on the C atoms in the pyrimidine li-

gand is smaller in the trans compound. In the cis- and trans-Pt(Y-

py)(pm)Cl₂complexes [10], the total average values of the four C

atoms are very similar in the two geometries. In the series

Pt(R₂SO)(pm)Cl₂[14], all the C atoms are more deshielded in the

The formation of a

r bond between the metal and the amine

should decrease the electron density on the ligand and there

should be a linear relation with the pKa of the protonated amine.

There does not seem to be any relation between the d(NH₂) chem-

ical shifts and the pKa of the protonated primary amines. The

experimental errors in NMR and the measurements of the pKa

are quite large and the pKa values were measured in a solvent dif-

ferent from the NMR spectra.

The proton afﬁnity measured in the gas phase should be a better

basicity indicator and it should inﬂuence the electron density on

the bonded amines. Fig. 1 shows the relation between the NMR

d(NH₂) of the complexes trans-Pt(amine)(pm)I₂versus the proton

afﬁnity for the four primary amines MeNH₂, EtNH₂, nPrNH₂and

nBuNH₂[36,37]. There seems to be a linear relationship as ex-

pected. An increase in the proton afﬁnity leads to a deshielding

of the amine group (d(NH₂)) in ¹H NMR.

cis geometry, probably because

p-bonding is very important in

the R₂SO–pm complexes and it is more effective in the cis

geometry.

Coupling with the ¹⁹⁵Pt isotope was observed for several com-

pounds. The ²J(¹⁹⁵Pt–¹³C₂) and ²J(¹⁹⁵Pt–¹³C₆) coupling constants

vary from 7 to 12 Hz, while the ⁴J(¹⁹⁵Pt–¹³C₄) are between 5 and

8 Hz. The ³J(¹⁹⁵Pt–¹³C₅) can usually give information on the geom-

etry of the Pt(II) compounds, but we could measure only one value

for the cis compounds (36 Hz). The values for the trans isomers are

between 29 and 34 Hz. Our results are consistent with the few

other reported compounds [10,14], which have shown smaller val-

ues for the trans complexes.

F.D. Rochon, H. Titouna / Inorganica Chimica Acta 363 (2010) 1679–1693

1687

Table 7

d(¹³C) (ppm) and J(¹⁹⁵Pt–¹³C) (Hz) of pm in cis- and trans-Pt(amine)(pm)I₂.

D

Amine

Geometry

C₂

C₆

C₄

C₅

Ave. Dd

Free pm (d)

NH₃

159.62

1.95

157.75

2.97 ²J = 7

5.53 ²J = 10

3.62 ²J = 7

5.38

157.75

1.91 ⁴J = 6

1.57

122.66

1.55

cis

trans

cis

trans

cis

2.10

3.08

2.22

2.78

1.95

3.09

3.04

3.02

3.04

2.00

2.69

2.76

3.01

2.11

3.04

2.79

3.04

2.11

2.95

4.35 ²J = 8

2.31 ²J = 9

4.24

0.87

MeNH₂

EtNH₂

1.47 ⁴J = 7

0.91

1.47 ³J = 36

0.62

2.01

4.35

2.93

1.82

1.03

trans

cis

trans

cis

trans

cis

5.53 ²J = 9

5.45 ²J = 10

5.44

1.57 ⁴J = 8

1.58

0.89 ³J = 34

0.87 ³J = 29

0.90

nPrNH₂

nBuNH₂

isoPrNH₂

Me₂NH

4.23 ²J = 7

4.20

1.56

4.22 ²J = 7

1.85

5.45

2.87

1.58 ⁴J = 8

1.82

1.44

0.56

0.63

3.87

4.17

5.10 ²J = 8

5.33

1.23

0.90

Et₂NH

cprNH₂

cbNH₂

4.25 ²J = 12

1.96

5.44 ²J = 7

2.98

1.51 ⁴J = 8

1.92

0.82 ³J = 33

1.56

4.23

5.46 ²J = 8

5.46 ²J = 10

5.46

1.58 ⁴J = 8

0.57 ⁴J = 5

1.57

0.89

0.90

cpNH₂

chNH₂

Ave.

4.24 ²J = 8

4.25

0.89 ³J = 33

1.41

2.02

3.07

1.79

Ave.

trans

4.22

5.42

1.34

0.81

The d(¹³C) of the amine ligands in the complexes are shown in

the experimental section, and the

d(¹³C) values are shown in Ta-

ble 8. We were not able to obtain the spectrum of cis-

Pt(cprNH₂)(pm)I₂, since it isomerized during the NMR measure-

ment. Several signals were found at higher ﬁelds than in the free

A few couplings of the amine C atoms with the ¹⁹⁵Pt isotope

were observed and they are shown in Table 8. The constants

²J(¹⁹⁵Pt–¹³C1) are 10 Hz, while the ³J(¹⁹⁵Pt–¹³C2) values are be-

tween 19 and 30 Hz for the trans compounds. No such coupling

could be observed for the the cis isomers. These results are similar

to those observed for Pt(amine)₂I₂[28,32].

D

amines. Therefore some

Dd values are negative. It is not possible

to compare the results on the different amines, since the local ef-

fects are too important in ¹³C NMR spectroscopy. We cannot dis-

cuss the results on the three amines which contained water and

the other results are not uniform. We do not have many data on

In order to determine if the ¹³C chemical shifts of the amines are

inﬂuenced by the basicity of the amine, a correlation study of d(C1)

and d(C2) versus the pKa of the protonated amines was done

(Figs. 2 and 3). A linear relationship was observed. An increase in

the basicity of the amine seems to induce a reduction of electron

density on C1 and C2 as expected. There is no correlation between

cis complexes. The long accumulation time caused the complete

P

isomerisation of several cis isomers. For MeNH₂, the sum

Dd is

smaller (more negative) for the cis isomer, for EtNH₂and Me₂NH,

the sum is larger for the cis compound, while for cbNH₂the sum

is identical for the two isomers.

the

D

d values and the pKa of the protonated primary amines. There

d(C1) with the pKa for

might be a correlation between d(C1) and

D

the secondary amines, but we have only two amines. A larger

quantity of secondary amines should be studied.

The ¹³C chemical shifts of several compounds cis- and trans-

Pt(amine)₂I₂were also found at higher ﬁelds than in the free

Fig. 4 shows the variation of d(C1) of the trans complexes versus

the proton afﬁnity for the four linear primary amines. There is a

linear relationship as expected. An increase of the proton afﬁnity

measured in the gas phase leads to a deshielding of the C1 signal

in ¹³C NMR.

amines [28,32] and only the complexes containing isoPrNH₂,

P

Me₂NH and Et₂NH showed positive

work.

Dd values as observed in this

Table 8

D

Pt(amine)(pm)I₂.

P

d(¹³C),

D

d

(ppm) and J(¹⁹⁵Pt–¹³C) (Hz) of the amines in cis- and trans-

3.1.2. I₂(nBuNH₂)Pt(l-pm)Pt(nBuNH₂)I₂

P

The cleavage of the diiodo-bridged dimer I(nBuNH₂)Pt(

I)₂Pt(nBuNH₂)I with pyrimidine produced two compounds, trans-

l

-

Amine

C1

C2

C3

C4

Dd

MeNH₂

Cis

Trans

ꢀ4.72

ꢀ2.82

ꢀ4.72

ꢀ2.82

60

nBuNH₂

EtNH₂

Cis

Trans

nPrNH₂trans

nBuNH₂trans

isoPrNH₂trans

isoPrNH₂

nPrNH₂

C1

C2

ꢀ1.42

ꢀ2.66

ꢀ3.09

ꢀ2.18

8.03

0.35

ꢀ1.07

ꢀ3.90

ꢀ3.87

ꢀ3.63

7.18

50

40

30

20

10

0

ꢀ1.24 ³J = 19

0.24

ꢀ1.02

ꢀ0.92

ꢀ0.22 ³J = 30

ꢀ0.85

ꢀ0.31

EtNH₂

MeNH₂

Me₂NH

Cis

Trans

Et₂NH trans

cprNH₂trans

nBuNH₂

6.76

4.89

6.76

4.89

5.08

nPrNH₂

6.06 ²J = 10

ꢀ0.98 ³J = 20

isoPrNH₂

a

EtNH₂

0.08

cbNH₂

Cis

Trans

cpNH₂trans

chNH₂trans

ꢀ1.82 ²J = 10

ꢀ1.79

0.38

0.37

ꢀ0.11

ꢀ1.11

ꢀ0.47

ꢀ1.55

ꢀ1.54

ꢀ1.74

ꢀ0.85

10.6

10.64

10.68

10.72

10.76

10.8

pKa

ꢀ0.64 ²J = 10

ꢀ1.46 ²J = 10

0.01 ³J = 21

1.00 ³J = 22

0.08

Fig. 2. d(C1) and d(C2) vs. pKa of the protonated aliphatic amines in trans-

a

hidden by the solvent.

Pt(RNH₂)(pm)I₂.

1688

F.D. Rochon, H. Titouna / Inorganica Chimica Acta 363 (2010) 1679–1693

Table 9

C1

NMR comparison of pyrimidine in trans-Pt(nBuNH₂)(pm)I₂and in I₂(nBuNH₂)Pt(

pm)Pt(nBuNH₂)I₂.

l-

70

60

50

40

30

20

10

0

cpNH₂

chNH₂

C2

cbNH₂

Dimer

³J(¹⁹⁵Pt–¹H,¹³C)

Trans monomer

³J(¹⁹⁵Pt–¹H,¹³C)

¹H NMR

cpNH₂

D

d H₂

d H₆

d H₄

d H₅

0.945

0.580

0.170

0.569

21

32

0.507

0.523

0.124

0.232

0.347

23

31

cprNH₂

Ave.

Dd

¹³C NMR

D

d C₂

d C₆

d C₄

d C₅

8.85

6.01

1.01

5.47

4.20

5.44

1.56

0.87

3.02

8.6 8.8

9

9.2 9.4 9.6 9.8 10 10.2

pKa

32

29

Ave.

Dd

Fig. 3. d(C1) and d(C2) vs. pKa for the protonated cyclic amines in trans-

Pt(RNH₂)(pm)I₂.

tween Pt(II) dimers containing chloro and iodo ligands will be

made in a later section of this paper.

60

nPrNH₂

nBuNH₂

The

coupling

constants

³J(¹⁹⁵Pt–¹H₂) = 21 Hz

and

50

40

30

20

10

0

³J(¹⁹⁵Pt–¹H_4,6) = 32 (Table 9). They are identical to those observed

for trans-Pt(nBuNH₂)(pm)I₂, suggesting a trans–trans conﬁguration

for the pyrimidine-bridged dimer. The ¹H NMR spectrum was

remeasured after several days in acetone at room temperature

and at 40 °C and no change was noted. It was remeasured again la-

ter and no isomerisation was observed, again suggesting the trans–

trans geometry, which is the most thermodynamically stable

conﬁguration.

EtNH₂

MeNH₂

The d(¹H) of the -NH₂protons in both the trans monomer and

the dimer were clearly observed. The signal is more deshielded

in the dimer (4.530 ppm) than in trans-Pt(nBuNH₂)(pm)I₂

(3.910 ppm). Furthermore, the coupling with the ¹⁹⁵Pt isotope

could be calculated. The ²J(¹⁹⁵Pt–¹HN) is 75 Hz in I₂(nBuNH₂)Pt-

910

915

920

925

930

935

PA(KJ/mole)

Fig. 4. d(C1) vs. the proton afﬁnity (PA) of the amine in trans-Pt(amine)(pm)I₂.

(l-pm)Pt(nBuNH₂)I₂and 68 Hz for trans-Pt(nBuNH₂)(pm)I₂. The

difference might not be signiﬁcant, since the signals are wide.

Pt(nBuNH₂)(pm)I₂(30%) and the pyrimidine-bridged dimer

I₂(nBuNH₂)Pt(l-pm)Pt(nBuNH₂)I₂(70%). In the latter compound,

The two amine signals are shown in Fig. 5.

the bridging ligand has the same symmetry as free pyrimidine

(Scheme 3). The atoms C₄and C₆are equivalent, as are H₄and H₆.

The ¹H NMR spectrum of the dimer has shown that the H-H

coupling pattern in the bridging ligand is identical to the one of

free pyrimidine. The ligand atoms are much deshielded upon coor-

dination, as shown in Table 9. The binding of the ligand to two Pt

atoms drastically reduces the electron density on the H and C

atoms. The most affected atoms are C₂and H₂. A comparison of

the NMR results with those of the monomer trans-Pt(nBuNH₂)(p-

3.2. The chloro complexes

3.2.1. Pt(amine)(pm)Cl₂

3.2.1.1. Synthesis. The compounds Pt(amine)(pm)Cl₂were synthe-

sized from the aqueous reaction of K[Pt(amine)Cl₃] with pyrimi-

dine. Two amines were chosen, a very bulky one, t-butylamine

(tBuNH₂) and a small amine, MeNH₂. K[Pt(tBuNH₂)Cl₃] was pre-

pared from the reaction of aqueous K₂[PtCl₄] with the amine by

the method already reported [20]. The experimental conditions

must be closely followed in order to decrease the formation of

Pt(tBuNH₂)₂Cl₂, which is very insoluble in aqueous medium. This

method cannot be used for less crowded amines, since cis-Pt(ami-

ne)₂Cl₂is produced too rapidly. K[Pt(MeNH₂)Cl₃] was prepared

from a long procedure, which we have published several years

ago [21], from the reaction of cis-Pt(MeNH₂)₂I₂via the diiodo-

bridged dimer as shown by the following equations:

m)I₂is also shown in Table 9. In ¹H NMR, the average

0.569 ppm for the dimer, while it is 0.347 ppm in the trans mono-

mer. In ¹³C NMR, the average

d value is 5.47 ppm for the dimer

and 3.02 ppm in the trans monomer. Our average

d(¹³C) value

for the dimer is larger than those reported for pm-bridged chloro

species in the literature. In (NBu₄)₂[Cl₃Pt( -pm)PtCl₃], the ave.

d = 2.76 ppm (in D₂O) [9], it is 2.6–4.2 ppm (in CD₂Cl₂) for

Dd value is

D

l

D

Cl₂(R₂SO)Pt(l-pm)Pt(R₂SO)Cl₂[9] and 3.3 to 3.8 ppm (in CDCl₃)

for Cl₂(Ypy)Pt(

l

-pm)Pt(Ypy)Cl₂[10]. Our larger values are proba-

bly caused by the presence of the iodo ligands. The comparison be-

2

C

3

N

1

N

Pt

C

4

6

C

5

Fig. 5. Coupling ²J(¹⁹⁵Pt–¹HN) in the dimer I₂(nBuNH₂)Pt(

and the monomer trans-Pt(nBuNH₂)(pm)I₂.

l-pm)Pt(nBuNH₂)I₂(left)

Scheme 3.

F.D. Rochon, H. Titouna / Inorganica Chimica Acta 363 (2010) 1679–1693

1689

the dichloro complexes. Only one band was observed for the trans

compounds at 338 cm^ꢀ1for the tBuNH₂complex and at 353 cm^ꢀ1

for trans-Pt(MeNH₂)(pm)Cl₂. Again, the vibration is at higher en-

ergy in the MeNH₂complex. The IR spectrum of the cis- et trans-

Pt(MeNH₂)(pm)Cl₂mixture has shown three

m(Pt–Cl) bands at

353, 350 et 347 cm^ꢀ1. The two bands at 350 and 347 cm^ꢀ1can

be assigned to the presence of the cis isomer.

The reaction with the silver salt is quite delicate and the pub-

lished procedure should be followed closely. No excess of silver

should ever be present, since it can react with the very reactive

aqua species, which are formed before the addition of KCl.

The neutral complexes Pt(amine)(pm)Cl₂were prepared from

the aqueous reaction of K[Pt(amine)Cl₃] with pyrimidine using a

pm/Pt ratio of 2/1. The yield for Pt(RNH₂)(pm)Cl₂is 73% for

tBuNH₂, but lower for MeNH₂(51%).

3.2.1.3. Multinuclear magnetic resonance spectroscopy. The NMR

spectra of the dichloro complexes were measured in acetone. The

¹⁹⁵Pt NMR spectra of the two trans compounds showed only one

signal conﬁrming the purity of the compounds, as also observed

in ¹H and ¹³C NMR. The signal of trans-Pt(tBuNH₂)(pm)Cl₂was ob-

served at slightly lower ﬁeld (ꢀ2125 ppm) than the one of trans-

Pt(MeNH₂)(pm)Cl₂(ꢀ2152 ppm). The difference (Dd = 27 ppm) is

probably caused by the solvent effect around the Pt(II) atom. The

d(Pt) are inﬂuenced by the weak binding of the molecules of sol-

vent on both sides of the Pt(II) plane, especially in solvents like

water and also to a smaller extent acetone. When one of the ligand

is very crowded close to its binding site like t-butylamine, the mol-

ecules of solvent cannot approach the metal atom as easily as with

a less crowded ligand like MeNH₂and the electron density of the

Pt(II) atom will be reduced. The reduction of molecules of solvent

in the close environment of the metal atom will therefore cause

a deshieding effect in ¹⁹⁵Pt NMR, as observed for related Pt(II) com-

plexes [16,28,32,33,39].

O

K½PtðamineÞCl₃ꢂ þ pm ^H!²PtðamineÞðpmÞCl₂# þKCl

Since the trans effect of the chloro ligand is larger than the one

of amines, the cis isomer should ﬁrst be formed. It has been shown

in the literature that cis compounds containing tBuNH₂isomerize

very rapidly to the trans conﬁguration, because of the bulkiness

of the amine. The cis ? trans isomerization is well known in the lit-

erature for the Pt(amine)₂X₂complexes, but usually it is performed

in an organic solvent (where the compounds are more soluble) like

acetone or by heating. With tBuNH₂, the bulkiness around the

binding atom is a very important factor and the cis ? trans rear-

rangement occurs in water. Therefore the product with this bulky

amine should produce trans-Pt(tBuNH₂)(pm)Cl₂.

A few studies were reported on the ¹⁹⁵Pt NMR spectra of the

compounds Pt(amine)₂Cl₂with aliphatic and cyclic amines

[32,40]. The reported d(Pt) vary from ꢀ2190 to ꢀ2225 ppm in ace-

tone for the cis complexes and between ꢀ2211 and ꢀ2237 ppm for

the trans complexes [32]. The trans complexes have been observed

at slightly higher ﬁelds than the cis analogs. The published values

vary slightly in other solvents [40]. The d(¹⁹⁵Pt) for trans-Pt(ami-

ne)(pm)Cl₂(ave. ꢀ2139 ppm) were observed at lower ﬁeld than

those for trans-Pt(amine)₂Cl₂[32]. The difference might be caused

For the smaller amine, cis-Pt(MeNH₂)(pm)Cl₂was expected, but

the characterization of the product has shown that it is a cis–trans

mixture. A proportion of ꢁ25% of the cis isomer was observed by

¹H NMR in acetone. The IR spectrum in the solid state has also

shown three m(Pt–Cl) bands, conﬁrming the presence of the two

isomers before dissolving the product in acetone. The cis isomer

is formed in the ﬁrst hours of reaction in water, but the reaction

was continued in order to increase the yield. After stirring for 16

hours at room temperature, the yield was 51%, but some isomeri-

sation had occurred. We believe that the proportion of the cis iso-

mer might have been larger than ꢁ25% in the solid state, but it

isomerized too rapidly in acetone (in the NMR tube) to detect its

real concentration. The compounds are insoluble in other more

neutral solvents like chloroform. The compound trans-

Pt(MeNH₂)(pm)Cl₂was obtained pure from the isomerization of

the mixture after 48 hours in acetone at room temperature.

The decomposition points of the pure compounds trans-Pt(ami-

ne)(pm)Cl₂have shown that the tBuNH₂compound is more stable

(220°–270°) than the MeNH₂analog (210°–230°). The MeNH₂mix-

ture has shown a color change at 190°, which probably corre-

sponds to the isomerisation of the cis isomer to the trans

compound.

by the presence of

p-bonding in the Pt–pm bond. Back-donation

(Pt ? pm) reduces the electron density on the Pt atom, thus shift-

ing its d(¹⁹⁵Pt) towards lower ﬁeld.

Dichloro complexes are much less soluble in organic solvents

than diiodo compounds. The long accumulation times required

for ¹⁹⁵Pt NMR spectroscopy did not permit the observation of the

signal of cis-Pt(MeNH₂)(pm)Cl₂, since it isomerized too rapidly in

the NMR tube.

As in the diiodo complexes discussed above, coordination of

pyrimidine to the metal reduces the symmetry of the ligand and

the protons H₆and H₄are in different environments_.The proton

H₂stays

a

singlet, H₆couples with H₅(³J = 5.7 Hz), H₄

(⁴J = 3.3 Hz) and H₂(⁴J = 1.2 Hz). H₄is a doublet of doublets with

³J(H₄–H₅) ꢁ4.8 Hz and ⁴J(H₄–H₆) = 2.1 Hz), while H₅couples with

H₄, H₆and H₂(1.2 Hz). The chemical shifts are listed in the exper-

imental section.

The

D

d values (d_complexꢀ d_pyrimidine) of the pyrimidine ligand

3.2.1.2. IR spectroscopy. The symmetry of pyrimidine in these com-

plexes has already been discussed for the diiodo complexes. The IR

absorption bands are listed in the experimental section and are

similar to those observed for the iodo analogs. The pyrimidine

vibrations vary slightly with the amines and are often found at

similar or slightly higher energies than in the free molecule.

and the coupling constants with ¹⁹⁵Pt are shown in Table 10. The

¹H NMR spectrum of trans-Pt(tBuNH₂)(pm)Cl₂has shown only

one species in solution and it did not vary with time, suggesting

a trans conﬁguration, as suggested also by the IR spectroscopic re-

sults. The ³J(¹⁹⁵Pt–¹H_2,6) values are 21 and 33 Hz, respectively, also

suggesting a trans geometry of the complex.

The stretching

m

(Pt–N) vibrations of the trans isomers were as-

The ¹H NMR spectrum of the isolated product

Pt(MeNH₂)(pm)Cl₂showed the presence of the two isomers

(ꢁ25% of the cis compound) in a fresh acetone solution. After the

complete isomerisation to the trans form in the NMR tube, the

assignments could be done. The signals of the cis isomer were ob-

signed to two weak bands observed at 420 and 462 cm^ꢀ1for the

tBuNH₂complex and at slightly higher energies (502 and

450 cm^ꢀ1) for trans-Pt(MeNH₂)(pm)Cl₂. For the Pt(MeNH₂)(pm)Cl₂

mixture, a single wide band centered around 445 cm^ꢀ1was

observed.

served at lower ﬁelds as shown in Table 10. The average

Dd of pm

The stretching

m(Pt–Cl) vibrations show usually strong absorp-

is larger for the cis isomer than for the trans compound (0.574 ver-

tion bands and they are very useful to determine the geometry of

sus 0.508 ppm).

1690

F.D. Rochon, H. Titouna / Inorganica Chimica Acta 363 (2010) 1679–1693

Table 10

D

d (ppm) and J(¹⁹⁵Pt–¹H,¹³C) (Hz) of Pt(amine)(pm)Cl₂.

Trans-Pt(tBuNH₂)(pm)Cl₂

J

Pt(MeNH₂)(pm)Cl₂

Cis

J

Trans

J

¹H NMR

D

d H₂

d H₆

d H₄

d H₅

0.303

0.335

0.136

0.135

0.227

³J = 21

³J = 33

0.665

0.626

0.455

0.550

0.574

d = 6.737

ꢀ0.264

³J = 27

0.547

0.584

0.404

0.496

0.508

d = 6.580

ꢀ0.32

³J = 18

³J = 31

Ave.

NH₂

D

d pm

D

d = 0.369

²J = 73

⁴J = 8

D

d CH₃

0.356

³J = 33

³J = 30

¹³C NMR

D

d C₂

d C₆

d C₄

d C₅

1.76

2.71

1.15

0.17

1.45

ꢀ2.07

8.25

²J = 16

²J = 10

⁴J = 9

2.60

3.02

2.43

1.29

2.33

ꢀ3.40

²J = 11

²J = 9

³J = 30

Ave.

Ddpm

D

d CH₃

d C1

³J = 18

²J = 13

d(¹⁹⁵Pt)

ꢀ2125

ꢀ2152

The coupling of H₂and H₆with ¹⁹⁵Pt could be well observed for

py)(pm)Cl₂[10]. The value of ⁴J(¹⁹⁵Pt–¹³C₄) (9 Hz) is in agreement

with the few related published values [10,14,29].

The NMR results on the chemical shifts of the amine ligands are

also shown in Table 10. For trans-Pt(tBuNH₂)(pm)Cl₂, the -NH₂

the trans isomer and they are as expected [10,14] for trans com-

pounds (18 and 31 Hz, respectively). The same couplings in the

cis complex were more difﬁcult to calculate because of the pres-

ence of the large quantity of the trans isomer in solution. The

³J(¹⁹⁵Pt–¹H₂) value was found to be 27 Hz, larger than the corre-

sponding value in the trans compound. Therefore it seems that

these coupling constants are larger in the cis compounds than in

the trans isomers, as observed in other Pt(II) compounds

[10,13,14,32].

group is deshielded upon coordination as expected with

D

a

d = 0.369 ppm and its ²J(¹⁹⁵Pt–¹H) coupling could be well ob-

served with a constant of 73 Hz. The corresponding value reported

for trans-Pt(tBuNH₂)₂I₂is ²J(¹⁹⁵Pt–¹H) = 58 Hz [28]. The coupling

constant ⁴J(¹⁹⁵Pt–¹H) with the –CH₃group is much smaller

(8 Hz). For the MeNH₂complexes, the –CH₃signal is a triplet due

to coupling with the -NH₂group with ³J(¹H–¹H) = 6.3 Hz and the

³J(¹⁹⁵Pt–¹H) value seems larger in the cis geometry (33 Hz) than

in the trans isomer (30 Hz).

Table 10 also shows that the ave.

Dd value is much larger for the

trans MeNH₂compound (0.508 ppm) than in the corresponding

tBuNH₂complex (0.227 ppm). We can also compare these values

with those obtained on the diiodo analogs. The values are much

In ¹³C NMR, the C1 atom located in

group in trans-Pt(tBuNH₂)(pm)Cl₂

d = 8.25 ppm), while the –CH₃group is shielded upon coordina-

tion (

a

position to the amine

larger in the dichloro MeNH₂compounds (ave.

and 0.506 (trans) ppm) than in the corresponding diiodo com-

plexes (ave. d = 0.339 (cis) and 0.196 (trans) ppm), which might

Dd = 0.574 (cis)

is very deshielded

(D

D

d = ꢀ2.07 ppm). It seems that the electron density on the

be attributed to the larger electronegativity of the chloro ions.

The C atoms of pyrimidine are observed at lower ﬁeld than in

the free molecule, indicating a reduction of electron density on

amine ligand is drastically changed upon coordination to the me-

tal. The ³J(¹⁹⁵Pt–¹³C) = 18 Hz, while the ²J(¹⁹⁵Pt–¹H) is smaller

(13 Hz).

the ligand upon coordination. The

important than the (Pt ? pm) bond if present. The deshielding is

more important in the MeNH₂complex (ave. d = 2.33 ppm) than

in the tBuNH₂analog (ave. d = 1.45 ppm). We can compare these

results with those observed in the diiodo series, For trans-

Pt(MeNH₂)(pm)I₂, the ave. d is 2.78 ppm, slightly larger than

the one observed for the dichloro analog. We do not have any val-

ues for cis-Pt(MeNH₂)(pm)Cl₂, since the long accumulation time

cause the complete isomerisation of the the cis complex.

r

(pm ? Pt) bond is much more

There are very few data on J(¹⁹⁵Pt–¹³C) couplings in the litera-

ture. In trans-Pt(tBuNH₂)₂I₂, the values ²J(¹⁹⁵Pt–¹³C1) = 9 and

³J(¹⁹⁵Pt–¹³C2) = 17 Hz [28]. The ²J values are usually smaller than

the ³J values, probably because of the inadequate orientation of

the different orbitals involved in the Pt–N–C group. Our values

are similar to those observed in related compounds [18,28,32,39].

In trans-Pt(MeNH₂)(pm)Cl₂, the –CH₃signal is shielded upon coor-

p

D

dination with

D

d = ꢀ3.40 ppm.

Several couplings were observed with the ¹⁹⁵Pt isotope. Only

one ³J(¹⁹⁵Pt–¹³C) value could be measured and these are usually

more important, since they can give information of the geometry

of the compound. For trans-Pt(tBuNH₂)(pm)Cl₂it is 30 Hz, very

similar to those observed for Pt(R₂SO)(pm)Cl₂, where values be-

tween 28 and 30 Hz were reported for the trans complexes and

around 40 Hz for the cis isomers [14]. For the Pt(Ypy)(pm)Cl₂

(Ypy = pyridine derivative) compounds [10], the reported values

are ꢁ38 (cis) and ꢁ29 Hz (trans). Our value agrees with those re-

ported for trans Pt(II) compounds. This coupling could not be ob-

3.2.2. Complexes trans,trans-Cl₂(amine)Pt(

l

-pm)Pt(amine)Cl₂

3.2.2.1. Synthesis and IR spectroscopy. The pyrimidine-bridged di-

mers were synthesized from the aqueous reactions of the ionic

compounds K[Pt(amine)Cl₃] with pyrimidine as described for the

preparation of Pt(amine)(pm)Cl₂, but using a Pt/pm ratio of 2/1.

The proportion must be respected in order to avoid the presence

of the mixed-ligands monomer. A crowded amine (tBuNH₂) and a

smaller one (MeNH₂) were chosen for the experiments. The reac-

tion time is one week for tBuNH₂and two days for MeNH₂.

served for trans-Pt(MeNH₂)(pm)Cl₂, even after

a

very long

O

2K½PtðamineÞCl₃ꢂþpm^H!²Cl₂ðamineÞPtð

l

-pmÞPtðamineÞCl₂þ2KCl

accumulation time, since this compound is less soluble than the

tBuNH₂analog. Several couplings ²J(¹⁹⁵Pt–¹³C) could be measured

and they are much smaller (10–16 Hz) as reported for pyridine

derivatives complexes [16,39], Pt(R₂SO)(pm)Cl₂[14] and Pt(Y-

Pyrimidine reacts with K[Pt(amine)Cl₃] to form the intermedi-

ate Pt(amine)(pm)Cl₂, which reacts with the Pt(II) atom of another

K[Pt(amine)Cl₃] molecule (Scheme 4) to form the pyrimidine-

F.D. Rochon, H. Titouna / Inorganica Chimica Acta 363 (2010) 1679–1693

1691

bridged dimer Cl₂(amine)Pt(

l

-pm)Pt(amine)Cl₂. Since the trans ef-

(ꢀ2125 ppm and ꢀ2152 ppm for amine = tBuNH₂and MeNH₂,

respectively). For the sulfoxide–pyrimidine analogs, the difference

between the trans monomers and the trans–trans dimers is about

10 ppm [9,14]. The latter dimers were found at slightly higher

ﬁelds, but sulfoxides are quite different from amines, since they

fect of the chloro ligand is larger than the one of the amine, cis

compounds are expected, but isomerisation is expected to occur

for the bulky amine tBuNH₂, leading to a trans–trans conﬁguration.

The intermediate Pt(tBuNH₂)(pm)Cl₂probably isomerized to the

trans isomer, before reacting with the second [Pt(tBuNH₂)Cl₃]^–

ion. For MeNH₂, a cis–cis isomer was expected. The ¹H NMR spectra

of a fresh solution of the two compounds have shown the presence

of only one species. Both molecules were eventually identiﬁed as

the trans–trans isomer. The reaction of the MeNH₂compound is

not very rapid and it was stopped after 2 days in order to reduce

the isomerisation, but the yield was not very high (61%). The

trans–trans geometry is the most thermodynamically stable conﬁg-

uration. The tBuNH₂dimer shows a higher thermal resistance

(decomposes between 225° and 260°) than the MeNH₂analog

(decomposes ꢁ200°).

form strong p-bonds with Pt(II).

The inﬂuence of the solvent can be observed in these two com-

plexes. The compound containing the bulky amine is observed at

lower ﬁeld than the one containing the smaller amine. The pres-

ence of bulkiness close to the binding site reduces the approach

on the molecules of solvent in the close environment of the metal

atom, which reduces the electron density on the Pt(II) atom. The

MeNH₂compound should permit more molecules of solvent to ap-

proach the Pt atom, thus increasing the electron density on the me-

tal atom. Its d(¹⁹⁵Pt) should be observed at slightly higher ﬁeld

than the one of the tBuNH₂analog. The difference is 18 ppm.

The symmetry of pyrimidine in these dimers is C_2v, the same as

in the free molecule (Scheme 3). Three signals are observed for the

pyrimidine ligand. H₂is a singlet because of the presence of the

two N neighboring atoms, while H₄et H₆are equivalent and are

The IR spectra of the two pyrimidine-bridged dimers were mea-

sured and the absorption bands are shown in the experimental sec-

tion. The symmetry of the bridging ligand is identical to the one of

free pyrimidine. Most of the vibrations are observed at slightly

higher energies than those in the free molecule. Those of the

tBuNH₂compound are very similar to those observed for the

monomer trans-Pt(tBuNH₂)(pm)Cl₂, while those of the MeNH₂di-

mer are at slightly higher energies than the ones in the correspond-

observed as

(⁴J(H_4,6–H₂) = 0.9 Hz). The H₅proton is the most shielded and is a

doublet of a triplet with J(H₅–H₂) = 1.5 Hz. The variations d in

¹H and ¹³C NMR are shown in Table 11, along with the average

d value. The atom H₂is much shifted to lower ﬁeld ( d_a-

a

doublet of doublets (³J(H_4,6–H₅) = 6.9 Hz and

D

ing trans monomer. Only one

m

(Pt–Cl) vibration was observed as

D

expected for a trans–trans conﬁguration. The band was observed

at higher energy for the tBuNH₂(342 cm^ꢀ1) than for the MeNH₂

analog (328 cm^ꢀ1). Three vibration bands were observed around

_ve.= 0.89 ppm) as expected from the binding of its two neighboring

N atoms to two metal centers. A more important deshielding is ob-

served than in the monomers, conﬁrming that the electron density

on the bridging ligand is lower than in the monodentate ligand.

The difference between the trans monomer and the dimer is much

larger for the tBuNH₂complexes than for the MeNH₂analogs as

shown in Table 11.

500 cm^ꢀ1, which could be attributed to the

m(Pt–N) stretching

vibrations [10,14,27–29,32]. These were observed at 502, 460,

422 cm^ꢀ1for the tBuNH₂complex and at 520, 503 and 495 cm^ꢀ1

for the MeNH₂analog.

The complexes are quite insoluble and it was difﬁcult to obtain

coupling constants with ¹⁹⁵Pt. A few could be measured are they

are shown in Table 11. The constants ³J(¹⁹⁵Pt–¹H₂) are 22 Hz, sim-

3.2.2.2. Multinuclear magnetic resonance spectroscopy. The ¹⁹⁵Pt

NMR spectra of the complexes Cl₂(amine)Pt(l-pm)Pt(amine)Cl₂

were measured in acetone. The compounds showed only one signal

indicating that the products are pure. The purity was also con-

ﬁrmed by ¹H and ¹³C NMR spectroscopy. The resonances were ob-

served at ꢀ2128 ppm and at ꢀ2146 ppm for the tBuNH₂and

MeNH₂complexes, respectively. These values are at the same ﬁeld

ilar to the results published for trans,trans-Cl₂(R₂SO)Pt(

l

-

pm)Pt(R₂SO)Cl₂(20–24 Hz) [9], for trans,trans-Cl₂(Ypy)Pt(

l

pm)Pt(Ypy)Cl₂(17–22 Hz) [10] and slightly larger than the value

reported for the complex trans,trans-Cl₂(PBu₃)Pt(l-pm)Pt(PBu₃)Cl₂

(15.8 Hz) [13]. The coupling constants ³J(¹⁹⁵Pt–¹H_4,6) are 30 and

33 Hz. The reported values are between 28 and 32 Hz for the

as

the

corresponding

monomer

trans-Pt(amine)(pm)Cl₂

Scheme 4.

1692

F.D. Rochon, H. Titouna / Inorganica Chimica Acta 363 (2010) 1679–1693

Table 11

D

d (ppm) and J(¹⁹⁵Pt–¹H,¹³C) (Hz) of pm and amine in trans,trans-Cl₂(amine)Pt(

l

-pm)Pt(amine)Cl₂.

Ave.

Amine

H₂C₂

H_4,6C_4,6

H₅C₅

0.220

D

d

Ave.

D

d trans monomer

NH₂

Amine

0.392

tBuNH₂¹H

³J(¹⁹⁵Pt–¹H)

¹³C

0.895

22

4.83

0.885

22

0.617

30

4.10

0.600

33

0.587

0.227

0.534

57

1.06

3.52

0.595

1.45

0.506

8.44, ꢀ1.88

ꢀ0.438

MeNH₂¹H

³J(¹⁹⁵Pt–¹H)

¹³C

0.294

d = 4.662

62

4.77

20

4.19

1.30

3.61

2.33

ꢀ3.93

²J(¹⁹⁵Pt–¹³C)

trans–trans R₂SO–pm dimers [9] and between 27 and 33 Hz for the

trans–trans Ypy–pm dimers [10]. The cis–cis dimers have shown

larger values [9].

erally larger in the cis conﬁguration than in the trans isomers.

These values are difﬁcult to measure because of the low solubility

of the complexes and they are more easily seen on a lower ﬁeld

instrument, because of chemical shift anisotropy. Furthermore,

the cis compounds isomerize in the NMR tube during the long

accumulation times and we do not have many values for cis com-

pounds. Our results have shown that all the ³J coupling constants

with the isotope ¹⁹⁵Pt are larger in the cis compounds than in the

trans analogs. A few couplings ²J(¹⁹⁵Pt–¹HN) could be measured

(average 68 Hz) for the trans isomers.

A few linear relationships between the NMR data and the pKa of

the protonated amines were observed. There are also some relation

between the proton afﬁnity (measured in the gas phase) of the

amine with some results observed in NMR spectroscopy.

The cleavage of the diiodo-bridged nBuNH₂dimer with pyrimi-

dine has produced two species, trans-Pt(nBuNH₂)(pm)I₂and the

The results in ¹³C NMR are also shown in Table 11. Again the

Dd

values are larger than in the monomers, conﬁrming a lower elec-

tron density on the bridging ligand. No coupling with the ¹⁹⁵Pt iso-

tope could be found for the tBuNH₂complex (due to its

insolubility), but ²J(¹⁹⁵Pt–¹³C₂) was observed for the MeNH₂com-

pound. The calculated value is 20 Hz. A few values ²J(¹⁹⁵Pt–¹³C_4,6

)

were reported for trans,trans-Cl₂(Ypy)Pt(l-pm)Pt(Ypy)Cl₂(be-

tween 13 and 15 Hz), but no ²J(¹⁹⁵Pt–¹³C₂) value was reported

for these dimers [10].

The chemical shifts of the amine ligands in the complexes are

also shown in Table 11. The -CH₃group of the MeNH₂ligand ap-

pears as a triplet due to coupling with the amine group. The C atom

in

a

position to the amine group is much deshielded upon coordi-

d = 8.44 ppm). The –NH₂groups

nation in the tBuNH₂compound (

D

pyrimidine-bridged dinuclear species I₂(nBuNH₂)Pt(l-pm)Pt-

were observed in both complexes with coupling constants

(nBuNH₂)I₂, which was identiﬁed as the trans–trans isomer. We

have made several experiments in order to synthesize these dimers

with the other amines, without success. It seems therefore that the

behavior of n-butylamine in these reactions is quite different. This

project should be continued in order to develop new methods to

synthesize these interesting pyrimidine-bridged iodo dimers with

other amines.

In the chloro series, two amines with different bulkiness were

studied. The compounds Pt(amine)(pm)Cl₂were synthesized from

the aqueous reaction of K[Pt(amine)Cl₃] with an excess of pyrimi-

dine. Only the trans monomer was observed for tBuNH₂, while a

cis–trans mixture was obtained with MeNH₂. The mixture isomer-

ized to the pure trans compound in acetone. The two compounds

²J(¹⁹⁵Pt–¹H₂N) of 57 and 62 Hz (Table 11).

4. Conclusion

Novel mixed-ligand Pt(II) complexes containing pyrimidine and

an amine were synthesized and characterized in the solid state by

IR spectroscopy and in acetone solution by multinuclear magnetic

resonance spectroscopy. Monomers of the types cis- and trans-

Pt(amine)(pm)X₂and pyrimidine-bridged dinuclear species

X₂(amine)Pt(l-pm)Pt(amine)X₂(X = I and Cl) were studied. The

diiodo complexes are more soluble in organic solvents than the

chloro analogs. Therefore they are more suited for solution NMR

studies. But IR spectroscopy gives more information on the geom-

trans-Pt(amine)(pm)Cl₂have shown only one m(Pt–Cl) stretching

vibration in IR spectroscopy, while the mixture has shown three

bands, of which two could be assigned to the cis isomer. Therefore

IR spectroscopy is a good indicator of the geometry of the dichloro

complexes.

When the aqueous reaction of K[Pt(amine)Cl₃] was performed

with pyrimidine in a 2:1 ratio, the pyrimidine-bridged dinuclear

etry of the dichloro complexes, since the

m(Pt–Cl) vibrations are

easier to measure than the corresponding

m(Pt–I) bands, which

are observed at much lower energy. The symmetry of pyrimidine

is C_2vfor the free molecule and in the bridging complexes, but it

is lowered when the ligand is monodentate as in Pt(amine)(pm)X₂.

Therefore NMR spectroscopy is an excellent method to differenti-

ate pyrimidine-bridged dimers from monomers.

In the iodo series, cis- and trans-Pt(amine)(pm)I₂were synthe-

sized from the cleavage of the diiodo-bridged dimer I(ami-

ne)Pt(l-I)₂Pt(amine)I with pyrimidine in water. The reactions

with several primary amines, two secondary amines and NH₃were

studied. MeNH₂produced pure cis-Pt(MeNH₂)(pm)I₂, while all the

other amines gave a cis–trans mixture or the pure trans isomer. The

cis compounds isomerize rapidly to the trans complex in acetone,

but also in aqueous medium (although more slowly), especially

those containing more bulky amines. Characterization by multinu-

clear magnetic resonance is not easy, since the compounds are not

soluble in neutral solvents like CDCl₃and scarcely soluble in ace-

tone. Long accumulation times are required especially for ¹⁹⁵Pt

and ¹³C NMR. Coupling of the isotopes ¹H and ¹³C are important

to measure, since their values can usually give information on

the geometry of the Pt(II) complex. The coupling constants are gen-

species Cl₂(amine)Pt(l-pm)Pt(amine)Cl₂, were obtained. Charac-

terization by IR and by multinuclear magnetic resonance spectros-

copies has shown that these dimers have the trans–trans geometry,

which is the most thermodynamically stable conﬁguration. Since

the trans effect of the chloro ligand is larger than the one of amines,

cis isomers were expected. With the bulky ligand tBuNH₂, isomeri-

sation should occur very rapidly. With the smaller amine MeNH₂,

the reaction time was increased to obtain a better yield, but cis ?

trans isomerization did occur. There might have been a small

amount of the cis-trans dinuclear compound, but it probably isom-

erized rapidly in acetone. Therefore, there was no evidence for the

presence of cis–cis ou cis–trans isomers.

Several couplings with ¹⁹⁵Pt could be observed for the dimers.

These values suggest a trans–trans conﬁguration based on the re-

ports of other related compounds.

The work should be extended to other amines. It might be inter-

esting to synthesize also mixed amine pyrimidine-bridged dimers

F.D. Rochon, H. Titouna / Inorganica Chimica Acta 363 (2010) 1679–1693

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1693

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ﬁnd the experimental conditions to isolate a mixed-geometry com-

pound such as trans,cis-Cl₂(tBuNH₂)Pt(l-pm)Pt(MeNH₂)Cl₂. The

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Acknowledgments

The authors are grateful to the Natural Sciences and Engineer-

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Article Doi

Synthesis and NMR characterization of the novel mixed-ligands Pt(II) complexes Pt(amine)(pyrimidine)X2 and trans,trans-X2(amine)Pt(μ-pyrimidine)Pt(amine)X 2 (X = I and Cl)

DOI: 10.1016/j.ica.2009.12.010

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Full text of DOI:10.1016/j.ica.2009.12.010

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